"building for observing astronomical phenomena," 1670s (in reference to Greenwich), from French observatoire, from observer (v.) "to observe, watch over, follow," from Latin observare "watch over," from ob "in front of, before" (see ob-) + servare "to watch, keep safe," from PIE root *ser- (1) "to protect."ETD observatory (n.).2

obsess (v.)

c. 1500, "to besiege" (a sense now obsolete), from Latin obsessus, past participle of obsidere "watch closely; besiege, occupy; stay, remain, abide" literally "sit opposite to," from ob "against" (see ob-) + sedere "to sit" (from PIE root *sed- (1) "to sit").ETD obsess (v.).2

In reference to evil spirits, "to haunt," from 1530s. The psychological sense of "to haunt as a fixed idea" developed gradually from 1880s and emerged 20c. The 1895 Century Dictionary has only the two senses "besiege" (marked obsolete) and "to attack, vex, or plague from without." Related: Obsessed; obsessing.ETD obsess (v.).3

obsessive (adj.)

"of or pertaining to obsession; liable to obsess," 1911, from obsess + -ive. As a noun, "person characterized by obsession," by 1966. Related: Obsessively. Obsessive-compulsive "combining (psychological) obsessions and compulsions" is attested from 1927.ETD obsessive (adj.).2

obsessed (adj.)

mid-15c., obcessed, "tormented, obsessed," past-participle adjective from obsess. Originally especially "possessed" by a devil or fiend.ETD obsessed (adj.).2

obsession (n.)

1510s, "action of besieging" (a sense now obsolete), from French obsession and directly from Latin obsessionem (nominative obsessio) "siege, blockade, a blocking up," noun of action from past-participle stem of obsidere "to besiege" (see obsess). Later (c. 1600), "hostile action of an evil spirit" (like possession but without the spirit actually inhabiting the body). Transferred sense of "action of anything which engrosses the mind" is from 1670s. Psychological sense "idea or image that intrudes on the mind of a person against his will" is from 1901.ETD obsession (n.).2

obsidian (n.)

"dark, hard, glass-like volcanic rock," 1650s, from Latin obsidianus, misprint of Obsianus (lapis) "(stone) of Obsius," name of a Roman alleged by Pliny to have found this rock in Ethiopia.ETD obsidian (n.).2

obsolescent (adj.)

"becoming obsolete, passing out of use," 1755, from Latin obsolescentum (nominative obsolescens), present participle of obsolescere "fall into disuse" (see obsolete).ETD obsolescent (adj.).2

obsolescence (n.)

"state or process of gradually falling into disuse, a becoming obsolete," 1809; see obsolescent + -ence. Phrase planned obsolescence was coined 1932, revived as a disparaging term 1950s.ETD obsolescence (n.).2

obsolesce (v.)

"fall into disuse, grow obsolete," 1801, from Latin obsolescere "to grow old, wear out, lose value, become obsolete," inchoative of obsolere "fall into disuse" (see obsolete). Related: Obsolesced; obsolescing.ETD obsolesce (v.).2

obsolete (adj.)

"that is no longer practiced or used, out of date, gone out of use, of a discarded type," 1570s, from Latin obsoletus "grown old, worn-out," past participle of obsolescere "fall into disuse, be forgotten about, become tarnished," which probably is from ob "away" (see ob-) + an expanded form of solere "to be used to, be accustomed" (see insolent).ETD obsolete (adj.).2

obstacle (n.)

"a hindrance, obstruction, impediment, or barrier; that which opposes or stands in the way," mid-14c., from Old French obstacle, ostacle "opposition, obstruction, hindrance" (13c.) and directly from Latin obstaculum "a hindrance, obstacle," with instrumental suffix *-tlom + obstare "stand before, stand opposite to, block, hinder, thwart," from ob "in front of, against" (see ob-) + stare "to stand," from PIE root *sta- "to stand, make or be firm."ETD obstacle (n.).2

Obstacle course "race course in which natural or artificial obstacles must be overcome" is attested by 1891.ETD obstacle (n.).3

obstetric (adj.)

"of or pertaining to a midwife or midwifery," 1742, from Modern Latin obstetricus "pertaining to a midwife," from obstetrix (genitive obstetricis) "midwife," literally "one who stands opposite (the woman giving birth)," from obstare "stand opposite to" (see obstacle). The true adjective would be obstetricic, "but only pedantry would take exception to obstetric at this stage of its career" [Fowler]. Related: Obstetrical.ETD obstetric (adj.).2

obstetrics (n.)

"science of midwifery, the department of medicine which deals with the treatment and care of women during pregnancy and childbirth," 1819, from obstetric (adj.); also see -ics.ETD obstetrics (n.).2

obstetrician (n.)

"one skilled in obstetrics," 1793, from Latin obstetricia "midwifery" (from obstetricus; see obstetric) on model of physician.ETD obstetrician (n.).2

obstinate (adj.)

"stubborn in adhering to one's own course, unyielding," late 14c., from Latin obstinatus "resolute, resolved, determined, inflexible, stubborn," past participle of obstinare "persist, stand stubbornly, set one's mind on," from ob "by" (see ob-) + stinare (related to stare "stand"), from PIE *ste-no-, from root *sta- "to stand, make or be firm." Related: Obstinately.ETD obstinate (adj.).2

obstinance (n.)

early 15c., obstinaunce, "non-compliance, self-willed persistence," from Medieval Latin obstinantia, from obstinatus "resolved, determined, resolute" (see obstinate). Earlier was obstinacioun "determination, resolution" (mid-14c.), from Old French.ETD obstinance (n.).2

obstinacy (n.)

late 14c., obstinacie, "hardness of heart, inflexibility of temper or purpose," from Medieval Latin obstinatia, from obstinatus "resolute, inflexible, stubborn" (see obstinate).ETD obstinacy (n.).2

obstipation (n.)

"action of blocking or stopping up," especially, in medicine, "constipation," 1590s, from Latin obstipationem (nominative obstipatio), noun of action from past-participle stem of *obstipare "action of blocking or stopping up," from ob "in front of; in the way of" (see ob-) + stipare "cram, pack, compress, surround" (see stiff (adj.)).ETD obstipation (n.).2

obstreperous (adj.)

"clamorous, noisy, boisterous, especially in opposition," c. 1600, from Latin obstreperus "clamorous," from obstrepere "drown with noise, make a noise against, oppose noisily," from ob "against" (see ob-) + strepere "make a noise," from PIE *strep-, said to be imitative (compare Latin stertare "to snore," Old Norse þrefa "to quarrel," þrapt "chattering, gossip," Old English þræft "quarrel"). But de Vaan writes, "It is uncertain that *strep- goes back to PIE, since it is only found in Latin and Germanic." Extended sense of "resisting control, management, or advice" is by 1650s. Related: Obstreperously; obstreperousness.ETD obstreperous (adj.).2

obstruction (n.)

"action of blocking up a way or passage, act of impeding passage or movement; fact of being obstructed," 1530s, from Latin obstructionem (nominative obstructio) "an obstruction, barrier, a building up," noun of action from past-participle stem of obstruere "build up, block, block up, build against, stop, bar, hinder," from ob "in front of, in the way of" (see ob-) + struere "to pile, build" (from PIE *streu-, extended form of root *stere- "to spread"). Figurative use is by 1650s.ETD obstruction (n.).2

obstructive (adj.)

"having the quality of obstructing, serving or intended to hinder, delay, or annoy," 1610s, from Latin obstruct-, past-participle stem of obstruere "to build up, block, block up, build against, stop, bar, hinder" (see obstruction) + -ive.ETD obstructive (adj.).2

obstruct (v.)

1610s, "to block or stop up with obstacles or impediments," a back-formation from obstruction or else from Latin obstructus, past participle of obstruere "build up, block, block up, build against, stop, bar, hinder," from ob "in front of, in the way of" (see ob-) + struere "to pile, build" (from PIE *streu-, extended form of root *stere- "to spread"). Figurative sense of "to hinder, impede, retard, delay" (justice, the law, etc.) is by 1640s. Related: Obstructed; obstructing.ETD obstruct (v.).2

obstructionism (n.)

"the practice of systematic or persistent obstruction," especially in a legislative body, 1868, from obstruction + -ism.ETD obstructionism (n.).2

obstructionist (n.)

"one who advocates or practices obstructionism, one who factiously opposes and hinders the action of others," 1846, from obstruction + -ist.ETD obstructionist (n.).2

obtainable (adj.)

"procurable, that may be got," 1610s, from obtain + -able. Related: Obtainability.ETD obtainable (adj.).2

obtain (v.)

early 15c., obteinen, "to get or acquire, inherit, gain, conquer," from Old French obtenir "acquire, obtain" (14c.) and directly from Latin obtinere "hold, hold fast, take hold of, get possession of, acquire," from ob "in front of" (though perhaps intensive in this case; see ob-) + tenere "to hold" (from PIE root *ten- "to stretch"). Intransitive sense of "be prevalent or customary, be established in practice" is from 1610s. Related: Obtained; obtaining.ETD obtain (v.).2

obtrude (v.)

1550s, "thrust forward forcibly or unduly" (trans.), from Latin obtrudere "to thrust into, press upon," from ob "in front of; toward" (see ob-) + trudere "to thrust," "to thrust, push," from PIE *treud- "to press, push, squeeze" (see threat). Intransitive sense of "be or become obtrusive, intrude, force oneself" is by 1570s. Related: Obtruded; obtruding.ETD obtrude (v.).2

obtrusion (n.)

"an undue and unsolicited thrusting forward of something upon the notice or attention of others," 1570s, from Latin obtrusionem (nominative obtrusio), noun of action from past-participle stem of obtrudere "to thrust into, press upon" (see obtrude).ETD obtrusion (n.).2

obtrusive (adj.)

"given to thrusting one's self or one's opinions upon the company or notice of others, characterized by forcibly thrusting (oneself, etc.) into notice or prominence," 1660s, from Latin obtrus-, past participle stem of obtrudere (see obtrude) + -ive. Related: Obtrusively; obtrusiveness.ETD obtrusive (adj.).2

obtund (v.)

c. 1400, obtunden, (transitive) "to render dead, make dull, blunt, deaden," used occasionally in English, especially in medical jargon; from Latin obtundere "to blunt, make dull, weaken, exhaust," literally "to beat against" (see obtuse). Related: Obtundation; obtunded.ETD obtund (v.).2

obtuse (adj.)

early 15c., "dull, blunted, not sharp," from Latin obtusus "blunted, dull," also used figuratively, past participle of obtundere "to beat against, make dull," from ob "in front of; against" (see ob-) + tundere "to beat," from PIE *(s)tud-e- "to beat, strike, push, thrust," from root *(s)teu- "to push, stick, knock, beat" (source also of Latin tudes "hammer," Sanskrit tudati "he thrusts"). Sense of "stupid, not acutely sensitive or perceptive" is by c. 1500. In geometry, in reference to a plane angle greater than a right angle," 1560s. Related: Obtusely; obtuseness.ETD obtuse (adj.).2

obverse (adj.)

"turned toward the observer, frontal," 1650s, from Latin obversus "turned against, directed toward," past participle of obvertere "to turn toward or against," from ob "toward" (see ob-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend"). According to OED, not in common use until the end of the 18th century. The noun, in reference to coins, medals, etc., "side on which the head or principal design is struck" (opposite of reverse), is attested from 1650s. Related: Obversely.ETD obverse (adj.).2

obviation (n.)

c. 1400, obviacioun "encounter, contact; exposure," from Medieval Latin obviationem (nominative obviatio), noun of action from past-participle stem of obviare "act contrary to, go against" (see obviate).ETD obviation (n.).2

obviate (v.)

1590s, "to meet and dispose of, clear (something) out of the way," from Late Latin obviatus, past participle of obviare "act contrary to, go against," from Latin obvius "that is in the way, that moves against," from obviam (adv.) "in the way," from ob "in front of, against" (see ob-) + viam, accusative of via "way" (see via). Related: Obviated; obviating.ETD obviate (v.).2

obvious (adj.)

1580s, "frequently met with" (a sense now obsolete), from Latin obvius "that is in the way, presenting itself readily, open, exposed, commonplace," from obviam (adv.) "in the way," from ob "in front of, against" (see ob-) + viam, accusative of via "way" (from PIE root *wegh- "to go, move, transport in a vehicle"). Meaning "plain to see, evident" is recorded from 1630s. Related: Obviously; obviousness.ETD obvious (adj.).2

oc-

assimilated form of ob- before -c-.ETD oc-.2

ocarina (n.)

simple musical instrument with a terra-cotta body, a mouthpiece, and finger-holes, 1877, from Italian ocarina, diminutive of oca "goose" (so called for its shape), from Vulgar Latin *auca, from Latin avicula "small bird," diminutive of avis "bird" (from PIE root *awi- "bird").ETD ocarina (n.).2

Occam's razor (n.)

when two competing hypotheses explain the data equally well, choose the simpler. Or, as Sir William Hamilton puts it, "Neither more, nor more onerous, causes are to be assumed, than are necessary to account for the phenomena." Named for English philosopher William of Ockham or Occam (c. 1285-c. 1349), "The Invincible Doctor," who expressed it with Entia non sunt multiplicanda praeter neccssitatem.ETD Occam's razor (n.).2

occasion (n.)

late 14c., occasioun, "opportunity; grounds for action or feeling; state of affairs that makes something else possible; a happening, occurrence leading to some result," from Old French ochaison, ocasion "cause, reason, excuse, pretext; opportunity" (13c.) or directly from Latin occasionem (nominative occasio) "opportunity, appropriate time," in Late Latin "cause," from occasum, occasus, past participle of occidere "fall down, go down," from ob "down, away" (see ob-) + -cidere, combining form of cadere "to fall" (from PIE root *kad- "to fall"). The notion is of a "falling together," or juncture, of circumstances. The sense of "the time or a time at which something happens" is from 1560s.ETD occasion (n.).2

occasion (v.)

mid-15c., occasionen, "to bring (something) about, be the cause of (something)," from occasion (n.), or else from Old French occasionner "to cause," from Medieval Latin occasionare, from Latin occasionem (see occasion (n.)). Related: Occasioned; occasioning.ETD occasion (v.).2

occasional (adj.)

late 14c., "occurring now and then," from occasion (n.) + -al (1) or from Old French ocasionel and directly from Medieval Latin occasionalis. Meaning "casual" is 1560s. Meaning "happening on or pertaining to a particular occasion" is from 1630s. Of furniture, etc., "adapted for use on special occasions," from 1749. Middle English had also occasionary "affording opportunity, favorable" (mid-15c.).ETD occasional (adj.).2

occasionally (adv.)

c. 1400, "happening on some particular occasion," also "sometimes, happening as occasion presents itself, without regularity," from occasional + -ly (2).ETD occasionally (adv.).2

occident (n.)

late 14c., "western part" (of the heavens or the earth), from Old French occident (12c.) or directly from Latin occidentem (nominative occidens) "western sky, sunset, part of the sky in which the sun sets," noun use of adjective meaning "setting," from present participle of occidere "fall down, go down" (see occasion (n.)). As a geopolitical term, sometimes with a capital O, always somewhat imprecise.ETD occident (n.).2

occidental (adj.)

c. 1400, "to, of, or in the west (of the sky or the earth)," from Old French occidental (14c.) and directly from Latin occidentalis "western," from occidentem (see occident). Meaning "of, pertaining to, or characteristic of the western regions of the earth (especially Western Europe and its derivative civilizations in the western hemisphere" (opposed to oriental), 1550s. As a capitalized noun meaning "a Western person" (opposed to Oriental) it is attested from 1823. Related: Occidentalism; occidentalist.ETD occidental (adj.).2

occipital (adj.)

"of, on, or in the back of the head," 1540s, from French occipital, from Medieval Latin occipitalis, from Latin occiput (genitive occipitis) "back of the skull," from assimilated form of ob "in the way of, against," here with a sense of "in back of" (see ob-) + caput "head" (from PIE root *kaput- "head"). As a noun, "the occipital bone," from 1758. Middle English had occiput (n.) "back of the head" and occipiciale (n.) "occipital bone."ETD occipital (adj.).2

Occitan (n.)

"Old or modern Provençal; langue d'Oc," 1940, also "the northern variant of modern Provençal;" from French oc, the word used south of the Loire for "yes" (see Languedoc).ETD Occitan (n.).2

occlude (v.)

"to shut up or stop up so as to prevent anything from passing through," 1590s, from Latin occludere (past participle occlusus) "shut up, close up," from assimilated form of ob "in front of, against" (see ob-) + claudere "to shut, close" (see close (v.)). Of teeth, "come in contact with another tooth," 1888. Related: Occluded; occluding.ETD occlude (v.).2

occlusion (n.)

"act or fact of being stopped up," 1640s, from Medieval Latin occlusionem (nominative occlusio), noun of action from past-participle stem of Latin occludere (see occlude). Dentistry sense "position of the two sets of teeth relative to each other when the mouth is closed" is from 1880.ETD occlusion (n.).2

occlusive (adj.)

"serving to close, having the function of closing," 1867, from Latin occlus-, past-participle stem of occludere (see occlude) + -ive.ETD occlusive (adj.).2

occult (adj.)

1530s, "secret, not divulged," from French occulte and directly from Latin occultus "hidden, concealed, secret," past participle of occulere "cover over, conceal," from assimilated form of ob "over" (see ob-) + a verb related to celare "to hide" (from PIE root *kel- (1) "to cover, conceal, save"). Meaning "not apprehended by the mind, beyond the range of understanding" is from 1540s. The association with the supernatural sciences (magic, alchemy, astrology, etc.) dates from 1630s. A verb occult "to keep secret, conceal" (c.1500, from Latin occultare) is obsolete.ETD occult (adj.).2

occultation (n.)

early 15c., occultacioun, "disguise or concealment of identity," from Latin occultationem (nominative occultatio), noun of action from past-participle stem of occultare "to hide, conceal," frequentative of occulere "to cover over, conceal" (see occult).ETD occultation (n.).2

occultism (n.)

"the doctrine, principles, or practices of occult sciences," 1870, from occult + -ism. Related: Occultist.ETD occultism (n.).2

occupation (n.)

early 14c., "fact of holding or possessing;" mid-14c., "a being employed in something," also "a particular action," from Old French occupacion "pursuit, work, employment; occupancy, occupation" (12c.), from Latin occupationem (nominative occupatio) "a taking possession; business, employment," noun of action from past-participle stem of occupare (see occupy). Meaning "employment, business in which one engages" is late 14c. That of "condition of being held and ruled by troops of another country" is from 1940.ETD occupation (n.).2

occupancy (n.)

1590s, "condition of being an occupant;" from occupant + abstract noun suffix -cy. Meaning "fact of occupying" is from 1833; that of "proportion of available space that is occupied" is attested by 1974.ETD occupancy (n.).2

occupant (n.)

1590s, "one who takes possession of something having no owner," from French occupant (15c.) or directly from Latin occupantem (nominative occupans), present participle of occupare "to take possession of" (see occupy). Earlier noun form was ocupier (early 14c.).ETD occupant (n.).2

occupational (adj.)

"of or pertaining to a particular occupation, calling, or trade," 1850, from occupation + -al (1). Occupational therapy is attested by 1918; occupational risk by 1951. Related: Occupationally.ETD occupational (adj.).2

occupier (n.)

late 14c., occupiour, "on who takes or holds possession" (of lands, manors, a benefice, etc.), agent noun from occupy.ETD occupier (n.).2

occupy (v.)

mid-14c., occupien, "to take possession of and retain or keep," also "to take up space or room or time; employ (someone)," irregularly borrowed from Old French ocuper, occuper "occupy (a person or place), hold, seize" (13c.) or directly from Latin occupare "take over, seize, take into possession, possess, occupy," from ob "over" (see ob-) + intensive form of capere "to grasp, seize," from PIE root *kap- "to grasp."ETD occupy (v.).2

The final syllable of the English word is difficult to explain, but it is as old as the record; perhaps it is from a modification made in Anglo-French. During 16c.-17c. the word was a common euphemism for "have sexual intercourse with" (a sense attested from early 15c.), which caused it to fall from polite usage.ETD occupy (v.).3

During the same time occupant could mean "prostitute." Related: Occupied; occupying.ETD occupy (v.).4

occupied (adj.)

late 15c., past-participle adjective from occupy (v.). Of countries overrun by others, from 1940, originally with reference to France.ETD occupied (adj.).2

occur (v.)

1520s, "meet, meet in argument," from French occurrer "happen unexpectedly" or directly from Latin occurrere "run to meet, run against, befall, present itself," from ob "against, toward" (see ob-) + currere "to run" (from PIE root *kers- "to run"). Sense development is from "meet" to "present itself" to "appear" to "happen" ("present itself in the course of events"). Meaning "to come into one's mind" is from 1620s. Related: Occurred; occurring.ETD occur (v.).2

occurrence (n.)

"that which presents itself, that which happens without design or expectation," 1530s, from French occurrence "unexpected happening" or directly from Medieval Latin occurrentia, from Latin occurentem (nominative occurens), present participle of occurrere (see occur). The adjective occurrent "occurring, happening, incidental" (mid-15c.) is long obsolete.ETD occurrence (n.).2

ocean (n.)

c. 1300, occean, "the vast body of water on the surface of the globe," from Old French occean "ocean" (12c., Modern French océan), from Latin oceanus, from Greek ōkeanos, the great river or sea surrounding the disk of the Earth (as opposed to the Mediterranean), a word of unknown origin; Beekes suggests it is Pre-Greek. Personified as Oceanus, son of Uranus and Gaia and husband of Tethys.ETD ocean (n.).2

In early times, when the only known land masses were Eurasia and Africa, the ocean was an endless river that flowed around them. Until c. 1650, commonly ocean sea, translating Latin mare oceanum. Application to individual bodies of water began 14c. (occean Atlantyke, 1387); five of them are usually reckoned, but this is arbitrary. The English word also occasionally was applied to smaller subdivisions, such as German Ocean "North Sea."ETD ocean (n.).3

oceanic (adj.)

"belonging or relating to the ocean," 1650s, probably from French océanique, from océan (see ocean).ETD oceanic (adj.).2

Oceania

"the southern Pacific islands and Australia, conceived as a continent," 1849, Modern Latin, from French Océanie (c. 1812). Apparently coined by Danish geographer Conrad Malte-Brun (1755-1826). Earlier in English as Oceanica (1832). Oceania was the name of one of the superstates in Orwell's "Nineteen Eighty-Four." Oceanea was the name of James Harrington's 17c. ideal state, and the name later was applied to the British empire. Related: Oceanean.ETD Oceania.2

oceanographer (n.)

"a student of the seas, one who systematically studies the ocean," 1886, agent noun from oceanography.ETD oceanographer (n.).2

oceanography (n.)

"the science of the oceans," 1859, coined in English from ocean + -graphy; on analogy of geography. French océanographie is attested from 1580s but is said to have been rare before 1876. Related: Oceanographic.ETD oceanography (n.).2

ocelot (n.)

"large wildcat of Central and South America," 1775, from French ocelot, a word formed by French naturalist Georges-Louis Leclerc, Comte de Buffon (1707-1788), from Nahuatl (Aztecan) ocelotl "jaguar" (in full tlalocelotl, a compound formed with tlalli "field").ETD ocelot (n.).2

ocher

see ochre.ETD ocher.2

ochlocracy (n.)

"government by the rabble," 1580s, from French ochlocratie (1560s), from Greek okhlokratia (Polybius) "mob rule," the lowest grade of democracy, from kratos "rule, power, strength" (see -cracy) + okhlos "(orderless) crowd, multitude, throng; disturbance, annoyance," which is probably literally "moving mass," from PIE *wogh-lo-, suffixed form of root *wegh- "to go, move." "Several possibilities exist for the semantic development: e.g. an agent noun *'driving, carrying, moving', or an instrument noun *'driver, carrier, mover'. ... An original meaning 'drive' could easily develop into both 'stirred mass, mob' and 'spiritual excitement, unrest'" [Beekes]. For sense development, compare mob (n.). Related: Ochlocrat, ochlocratic; ochlocratical. Greek also had okhlagogos "mob-leader, ochlagogue."ETD ochlocracy (n.).2

ochre (n.)

common name of a type of clayey soil much used in pigments, late 13c., oker, ocre, from Old French ocre (c. 1300) and directly from Medieval Latin ocra, from Latin ochra, from Greek khra, from khros "pale yellow," a word of unknown origin. It consists hydrated sesquioxids of iron mixed with various earthy materials, principally silica and alumina. As a color name, "brownish-yellow," it is attested from mid-15c. Related: Ochreous.ETD ochre (n.).2

o'clock (adj.)

phrase preceded by one, two, three, etc., and signifying the time of day as shown by the face of a clock, c. 1720, an abbreviation of of the clock, from Middle English of the clokke (late 14c.). See O + clock (n.). The use of clock hand positions to describe vector directions or angles is from late 18c.ETD o'clock (adj.).2

-ocracy

word-forming element; -cracy with a connective -o-.ETD -ocracy.2

octa-

before vowels oct-, word-forming element meaning "eight," from Greek okta-, okt-, from PIE *okto(u) "eight" (see eight). The variant form octo- often appears in words taken from Latin, but the Greek form is said to be the more common in English.ETD octa-.2

octad (n.)

"a group, system, or series of eight," 1801; see octa- + -ad.ETD octad (n.).2

octagon (n.)

in geometry, "a plane figure having eight angles and eight sides," 1650s, from Latin octagonos, from Greek oktagōnos, literally "eight-angled, eight-cornered," from okta- combining form of okto "eight" (see eight) + gōnia "angle," which is related to gony "knee" (from PIE root *genu- (1) "knee; angle"). Also octogon (1650s), from French octogone.ETD octagon (n.).2

octagonal (adj.)

"eight-sided and eight-angled," 1570s, from octagon + -al (1).ETD octagonal (adj.).2

octahedron (n.)

"a solid figure bounded by eight plane faces," 1560s, from Greek oktahedron, neuter of oktahedros "eight-sided," from okta- "eight" (see octa-) + hedra "a seat; face of a geometrical solid," from PIE root *sed- (1) "to sit." Related: Octahedral.ETD octahedron (n.).2

octane (n.)

hydrocarbon of the methane series, 1872, coined from oct- "eight" (see octa-) + -ane; so called because it has eight carbon atoms. A fuel's octane rating, in reference to its anti-knocking quality, is attested from 1932.ETD octane (n.).2

octant (n.)

instrument for making angular measurements in navigation or astronomy, 1731, from Late Latin octans "the eighth part," from octo "eight" (see octa-) on analogy of quadrant. In geometry, "the eighth part of a circle," by 1750.ETD octant (n.).2

octave (n.)

c. 1300, utaves (plural, via Anglo-French from popular Old French form oitieve, otaves), reformed in early 15c., from Medieval Latin octava, from Latin octava dies "eighth day," fem. of octavus "eighth," from octo (see eight).ETD octave (n.).2

Originally "period of eight days after a festival," also "eighth day after a festival" (counting both days, by inclusive reckoning; thus if the festival was on a Sunday, the octaves would be the following Sunday).ETD octave (n.).3

Verse sense of "stanza of eight lines" is from 1580s; musical sense of "note eight diatonic degrees above (or below) a given note" is by 1650s, from Latin octava (pars) "eighth part." Formerly English eighth was used in this sense (mid-15c.)ETD octave (n.).4

Octavia

fem. proper name, from Latin, fem. of Octavius, literally "the eighth" (see Octavian).ETD Octavia.2

Octavian

masc. proper name, from Latin, from Octavius, from octavus "eighth," from octo (see eight).ETD Octavian.2

octavo (n.)

1580s, printer's word for sheets folded to make eight leaves, from Latin in octavo "in the eighth," ablative of octavus "eighth" from octo "eight" (see eight, and compare octave). Abbreviation is 8vo.ETD octavo (n.).2

octo-

word-forming element, before vowels oct-, from combining form of Latin octo "eight," from PIE root *octo(u)- "eight" (see eight). Words made from Greek elements or derived from Greek typically are octa-.ETD octo-.2

October

late Old English, from Latin October (mensis), from octo "eight," from PIE root *octo(u)- "eight" (see eight). The eighth month of the old Roman calendar (pre-46 B.C.E.), which began the year in March. For -ber see December. Replaced Old English winterfylleð. In Russian history, the October Revolution (in which the Bolsheviks overthrew the Provisional Government) happened Nov. 7, 1917, but because Russia had not at that time adopted the Gregorian calendar reform, this date was reckoned there (Old Style) as Oct. 25.ETD October.2

Octobrist (n.)

1., from Russian oktyabrist, "member of the league formed October 1905 in response to imperial policies"; 2., from Russian Oktyabryonok, "member of a Russian communist children's organization founded 1925 and named in honor of the October Revolution." See October + -ist.ETD Octobrist (n.).2

octogenarian (n.)

"person 80 years old or 80-odd years of age," 1789, with -an + French octogénaire "aged 80," from Latin octogenarius "containing eighty," from octogeni "eighty each," related to octoginta "eighty," from octo "eight" (see eight) + -genaria "ten times," from PIE *dkm-ta-, from root *dekm- "ten." As an adjective, "eighty years of age," from 1784. An earlier adjective was octogenary (1690s).ETD octogenarian (n.).2

octopod

1826 (adj.), "eight-footed or eight-armed;" 1835 (n.) "an eight-footed or eight-armed animal," especially an octopus, from Latinized form of Greek oktōpod-, stem of oktōpous (see octopus).ETD octopod.2

octopus (n.)

1758, genus name of a type of eight-armed cephalopod mollusks, from Latinized form of Greek oktōpous, literally "eight-foot," from oktō "eight" (see eight) + pous "foot," from PIE root *ped- "foot."ETD octopus (n.).2

The more usual Greek word seems to have been polypous (also pōlyps), from polys "many" + pous, but for this word Thompson ["Glossary of Greek Fishes," 1947] suggests folk-etymology and a non-Hellenic origin.ETD octopus (n.).3

The classically correct Greek plural (had the word been used in this sense in ancient Greek) would be octopodes. Octopi (1817) regards the -us in this word as the Latin noun ending that takes -i in plural. Like many modern scientific names of creatures, it was formed in Modern Latin from Greek elements, so it might be allowed to partake of Latin grammar in forming the plural. But it probably is best to let such words follow the grammar of the language that uses them, and octopuses probably works best in English (unless one wishes also to sanction diplodoci for the dinosaurs).ETD octopus (n.).4

Used figuratively since at least 1882 of powers having far-reaching influence (usually as considered harmful and destructive). To the ancients, the octopus was crafty and dangerous, thrifty (stores food in its nest), and proverbial of clever and adaptable men, based on the animal's instinct of changing color when frightened or for disguise.ETD octopus (n.).5

It also was thought to be amphibious and to climb trees near shores to steal grapes and olives (the giant ones were said to raid whole warehouses). Thompson writes that "the eggs look remarkably like ripe olives; hence the story."ETD octopus (n.).6

octoroon (n.)

"offspring of a quadroon and a white," 1861, an irregular formation from Latin octo "eight" (see eight) + suffix abstracted from quadroon (in which the suffix actually is -oon). So called for having one-eighth Negro blood.ETD octoroon (n.).2

octuple (adj.)

"eightfold," c. 1600, from Latin octuplus "eightfold," from octo "eight" (see octo-) + -plus "-fold" (see -plus).ETD octuple (adj.).2

ocular (adj.)

c. 1500, "of or pertaining to the eye," from Late Latin ocularis "of the eyes," from Latin oculus "an eye," from PIE root *okw- "to see." As a noun, "eyepiece of an optical instrument," 1835, from the adjective.ETD ocular (adj.).2

oculist (n.)

"eye doctor," 1610s, from French oculiste (16c.), from Latin oculus "an eye" (from PIE root *okw- "to see"). Middle English had oculister (early 15c.) "an authority on the eye and treatment of eye diseases."ETD oculist (n.).2

oculus (n.)

"an eye," plural oculi, 1857, from Latin oculus "an eye" (from PIE root *okw- "to see").ETD oculus (n.).2

O.D.

abbreviation of overdose, attested from 1960.ETD O.D..2

ode (n.)

1580s, from French ode (c. 1500), from Late Latin ode "lyric song," from Greek ōidē, an Attic contraction of aoidē "song, ode;" related to aeidein (Attic aidein) "to sing;" aoidos (Attic oidos) "a singer, singing;" aude "voice, tone, sound," probably from a PIE *e-weid-, perhaps from root *wed- "to speak." In classical use, "a poem intended to be sung;" in modern use usually a rhymed lyric, often an address, usually dignified, rarely extending to 150 lines. Related: Odic.ETD ode (n.).2

oda (n.)

room in a harem, 1620s, from Turkish odah "hall, chamber."ETD oda (n.).2

odalisque (n.)

"female slave or concubine in a harem," 1680s, from French odalisque (1660s), from Turkish odaliq "maidservant," from odah "room in a harem," literally "chamber, hall," + -liq, suffix expressing function. In French, the suffix was confused with -isque, which is ultimately from Greek -isk(os) "of the nature of, belonging to."ETD odalisque (n.).2

odds (n.)

in wagering, "equalizing allowance to a weaker side or player by a stronger, advantage conceded by one of the parties in proportion to the assumed chances in his favor," 1590s, found first in Shakespeare ("2 Henry IV," 1597), probably from the word's earlier sense of "condition of inequality, difference, amount by which one thing exceeds or falls short of another" (1540s), from odd (q.v.), though the exact sense evolution is uncertain. Odds was used for "unequal things, matters, or conditions" from c. 1500, and the later senses may have evolved generally from this earlier notion of "things that don't come out even."ETD odds (n.).2

Until 19c. treated as a singular, though obviously a plural (compare news). General sense of "chance or balance of probability in favor of something happening" is by 1580s. Sense of "disagreement, variance, strife" (1580s) is the notion in at odds "at controversy or quarrel, unable to agree." Odds-on "on which the odds are laid" is by 1890.ETD odds (n.).3

oddness (n.)

late 14c., oddenesse, "unevenness of number," from odd + -ness. Meaning "strangeness, queerness, divergence from what is ordinary or useful" is from 1610s.ETD oddness (n.).2

O — observable (adj.)

odd (adj.) — ogress (n.)