A- (3) prefix meaning "not," from Gk a-, an- "not," from pie base *ne "not" (see un-)

O --- blood type, 1926, originally "zero," denoting absence of A and B agglutinogens.

o --- interj. of fear, surprise, admiration, etc., see oh.

O' --- as a prefix in Irish names, from Ir. ó, ua (O.Ir. au) "descendant."

O.D. --- abbreviation of overdose, attested from 1960.

oaf --- 1610 (implied in oafish), also auf (1621), "a changeling; a foolish child left by the fairies" [Johnson], from a Scand. source, cf. Norw. alfr "silly person," in O.N., "elf" (see elf). Hence, "a misbegotten, deformed idiot." Until recently, some dictionaries still gave the plural as oaves.

oak --- O.E. ac "oak tree," from P.Gmc. *aiks (cf. O.N. eik, O.Fris., M.Du. ek, Du. eik, O.H.G. eih, Ger. Eiche), of uncertain origin with no certain cognates outside Gmc. The usual I.E. base for "oak" (*derwo-/*dreu-) has become Mod.Eng. tree. Used in Biblical translations to render Heb. elah (probably usually "terebinth tree") and four other words. The O.N. form was eik, but there were no oaks in Iceland so the word came to be used there for "tree" in general.

oakum --- loose fiber obtained from taking apart old hemp ropes, 1420s, from O.E. acumba "tow, oakum, flax fibers separated by combing," lit. "what is combed out," from a- "away, out, off" + stem of cemban "to comb," from camb "a comb;" from P.Gmc. *us-kambon, second element from PIE *gembh- "tooth, nail" (see comb).

oar --- O.E. ar (said to be from O.N. ar), from P.Gmc. *airo; perhaps rel. to L. remus "oar," Gk. eretes "rower," eretmos "oar."

oasis --- 1613, from Fr., from L.L., from Gk. oasis, probably from Hamitic (cf. Coptic wahe, ouahe "dwelling place, oasis," from ouih "dwell"). The same Egyptian source produced Arabic wah.

oat --- O.E. ate "grain of the oat plant" (pl. atan), possibly from O.N. eitill "nodule," denoting a single grain, of unknown origin. The usual Gmc. name is derived from P.Gmc. *khabran (cf. O.N. hafri, Du. haver, source of haversack). Famously defined by Johnson as, "A grain, which in England is generally given to horses, but in Scotland supports the people." Wild oats, "crop that one will regret sowing," is first attested 1564, in ref. to the folly of sowing these instead of good grain.

oath --- O.E. að "oath, judicial swearing, solemn appeal to deity in witness of truth or a promise," from P.Gmc. *aithaz (cf. O.N. eiðr, Swed. ed, O.Fris. eth, Du. eed, Ger. eid, Goth. aiþs "oath"), from PIE *oi-to- "an oath" (cf. O.Ir. oeth "oath"). In ref. to careless invocations of divinity, from c.1175.

oatmeal --- 1393, from oat (q.v.) + M.E. mele (see meal (2)).

ob- --- prefix meaning "toward, against, across, down," also used as an intensive, from L. ob "toward, against, in the way of, about, before," from PIE base *opi- (cf. Oscan op, Gk. opi- "behind," Hittite appizzis "younger," Lith. ap- "about, near," Gk. epi "on, upon").

Obadiah --- masc. proper name, fourth of the Twelve Prophets of the O.T., from Heb. Obhadyah, lit. "servant of the Lord."

obbligato --- musical instruction, 1724, from It., lit. "obligated," from L. obligatus, pp. of obligare "to bind" (see oblige).

obdurate --- c.1440, from L. obduratus "hardened," pp. of obdurare "harden," from ob "against" + durare "harden, render hard," from durus "hard" (see endure).

obeah --- sorcery, witchcraft among blacks in Africa and the W.Indies, 1760, from a W. African word, cf. Efik (southern Nigeria) ubio "a thing or mixture left as a charm to cause sickness or death," Twi ebayifo "witch, wizard, sorcerer."

obedient --- c.1225, from O.Fr. obedient (11c.), from L. obedientem (nom. obediens), prp. of oboedire "to obey" (see obey). Obedience in ref. to dog training is attested from 1930.

obeisance --- c.1374, "act or fact of obeying," from O.Fr. obeissance "obedience," from obeissant, prp. of obeir "obey," from L. oboedire (see obey). Sense in Eng. alt. late 14c. to "bending or prostration of the body as a gesture of submission or respect" by confusion with abaisance.

obelisk --- rectangular stone column, tapering at the top, 1569, from M.Fr. obélisque, from L. obeliscus "obelisk, small spit," from Gk. obeliskos, dim. of obelos "a spit, pointed pillar, needle."

Oberon --- king of the faeries and husband of Titania in medieval lore, from Fr. Obéron, from O.Fr. Auberon, perhaps from a Gmc. source related to elf.

obesity --- 1611, from Fr. obésité, from L. obesitas "fatness, corpulence," from obesus "that has eaten itself fat," pp. of obdere "to eat all over, devour," from ob "over" + edere "eat" (see edible). The adj. obese is attested from 1651.

obey --- c.1290, from O.Fr. obeir, from L. oboedire "obey, pay attention to, give ear," lit. "listen to," from ob "to" + audire "listen, hear" (see audience). Same sense development is in cognate O.E. hiersumnian.

obfuscate --- 1536, from L. obfuscatus, pp. of obfuscare "to darken," from ob "over" + fuscare "to make dark," from fuscus "dark."

Obie --- one of the annual awards given to off-Broadway theater, 1967, from O.B. as the abbreviation of Off-Broadway.

obit --- c.1375, "death," from L. obitus "death," pp. of obire, lit. "to go toward" (see obituary). In modern usage (since 1874) it is usually a clipped form of obituary, though it had the same meaning of "published death notice" 15c.-17c. The scholarly abbreviation ob. with date is from L. obiit "(he) died," third person sing. of obire.

obiter --- 1573, from L., lit. "by the way," from ob "to, toward" + iter "journey" (see ion); hence obiter dictum (1812) "statement in passing," a judge's expression of opinion not regarded as binding or decisive.

obituary --- 1706, "register of deaths," from M.L. obituarius "a record of the death of a person," lit. "pertaining to death," from L. obitus "departure, a going to meet, encounter" (a euphemism for "death"), from stem of obire "go to meet" (as in mortem obire "meet death"), from ob "to, toward" + ire "go." Meaning "record or announcement of a death, esp. in a newspaper, and including a brief biographical sketch" is from 1738. A similar euphemism is in O.E. cognate forðfaran "to die," lit. "to go forth."

object (n.) --- 1398, "tangible thing, something perceived or presented to the senses," from M.L. objectum "thing put before" (the mind or sight), neut. of L. objectus, pp. of obicere "to present, oppose, cast in the way of," from ob "against" + jacere "to throw" (see jet). Sense of "thing aimed at" is c.1386. No object "not a thing regarded as important" is from 1782. Object lesson "instruction conveyed by examination of a material object" is from 1831.

object (v.) --- c.1400, "to bring forward in opposition," from L. objectus, pp. of objectare "to cite as grounds for disapproval," freq. of obicere, or else lit. "to put or throw before or against" (see object (n.)).

objection --- c.1380, from O.Fr. objection (12c.), from M.L. obiectionem (nom. obiectio), "a throwing or putting before," noun of action from L. obicere "to oppose" (see object (n.)). Objectionable first attested 1781.

objective --- 1620, originally in the philosophical sense of "considered in relation to its object" (opposite of subjective), formed on pattern of M.L. objectivus, from objectum "object" (see object (n.)). Meaning "impersonal, unbiased" is first found 1855, influenced by Ger. objektiv. The noun is 1738, with sense of "something objective to the mind;" meaning "goal, aim" is first as a military term from the U.S. War Between the States, 1864 (in objective point), from Fr.; general use of it is first attested 1881. Objectivism in philosophical sense of "the doctrine that knowledge is based on objective reality" is first attested 1854.

objet --- an object on display, an ornament, 1857, from Fr., especially in objet d'art (1865).

oblate (adj.) --- flattened on the ends, 1705, from L. ob "toward" + latus, abstracted from its opposite, prolatus "lengthened" (see oblate (n.)).

oblate (n.) --- person devoted to religious work, 1756, from M.L. oblatus, noun use of L. oblatus, variant pp. of L. offerre "to offer, to bring before" (latus "carried, borne" used as suppletive pp. of ferre "to bear"), from *tlatos, from PIE base *tel-, *tol- "to bear, carry" (see extol).

oblation --- 1412, from O.Fr. oblation "offering, sacrifice," from L. oblationem (nom. oblatio) "an offering, presenting, gift," in L.L. "sacrifice," from L. oblatus (see oblate (n.)).

obligation --- 1297, from O.Fr. obligation (1235), from L. obligationem (nom. obligatio) "an engaging or pledging," lit. "a binding" (but rarely used in this sense), noun of action from obligare (see oblige). The notion is of binding with promises or by law or duty. Oblige, with which it is usually confused, means "to do one a favor."

oblige --- 1297, "to bind by oath," from O.Fr. obligier, from L. obligare, from ob "to" + ligare "to bind," from PIE base *leig- "to bind" (see ligament). Main modern meaning "to make (someone) indebted by conferring a benefit or kindness" is from 1567; be obliged "be bound by ties of gratitude" is from 1548. Obliging "willing to do service or favors" is attested from 1632.

oblique --- 1432, from M.Fr. oblique, from L. obliquus "slanting, sidelong, indirect," from ob "against" + root of licinus "bent upward," from PIE base *lei- "to bend, be movable" (see limb (1)). As a type of muscles, in ref. to the axis of the body, 1615 (adj.), 1800 (n.).

obliterate --- 1600, from L. obliteratus, pp. of obliterare "cause to disappear, efface," from ob "against" + littera (also litera) "letter, script" (see letter); abstracted from phrase literas scribere "write across letters, strike out letters."

oblivion --- 1390, "state or fact of forgetting," from L. oblivionem (nom. oblivio) "forgetfulness," from oblivisci (pp. oblitus) "forget," originally "even out, smooth over," from ob "over" + root of levis "smooth." Oblivious is c.1450, from L. obliviosus "forgetful," from oblivio. It has lost its original sense of "no longer aware or mindful," however, and now means simply "unaware" (1862). Properly should be used with to, not of.

oblong --- c.1420, from L. oblongus originally "somewhat long," from ob "to, toward" + longus "long" (see long (adj.)).

obloquy --- 1460, "evil speaking," from L.L. obloquium "speaking against, contradiction," from ob "against" + loqui "to speak," from PIE *tolkw-/*tlokw- "to speak."

obnoxious --- 1581, from L. obnoxiosus "hurtful, injurious," from obnoxius "subject to harm," from ob "to, toward" + noxa "injury, hurt, damage entailing liability" (see noxious). Originally "subject to authority, subject to something harmful;" meaning "offensive, hateful" is first recorded 1675, influenced by noxious (q.v.).

oboe --- 1724, from It. oboe, from M.Fr. hautbois (itself borrowed in Eng. 16c. as hautboy), from haut "high" + bois "wood" (see bush). So called because it had the highest register among woodwind instruments.

obol --- ancient Gk. small coin and weight, 1670, from Gk. obolos, identical with obelos "a spit, needle." From the original shape.

obscene --- 1593, "offensive to the senses, or to taste and refinement," from M.Fr. obscène, from L. obscenus "offensive," especially to modesty, originally "boding ill, inauspicious," perhaps from ob "onto" + cænum "filth." Meaning "offensive to modesty or decency" is attested from 1598. Legally, in U.S., it hinged on "whether to the average person, applying contemporary community standards, the dominant theme of the material taken as a whole appeals to a prurient interest." [Justice William Brennan, "Roth v. United States," June 24, 1957]; refined in 1973 by "Miller v. California":

obscure (adj.) --- c.1400, from O.Fr. obscur "dark, dim, not clear," from L. obscurus "covered over, dark, obscure, indistinct," from ob "over" + -scurus "covered," from PIE *(s)keu- "to cover, conceal;" source of O.N. sky, O.E. sceo "cloud," and L. scutum "shield" and Gk. skeue "dress" (see sky). The verb is first recorded 1432. Obscurity is attested from 1481 in sense of "absence of light;" 1619 with meaning "condition of being unknown." Obscurantism (1834) is from Ger. obscurantismus (18c.).

obsequious --- c.1450, "prompt to serve," from L. obsequiosus "compliant, obedient," from obsequium "compliance, dutiful service," from obsequi "to accommodate oneself to the will of another," from ob "after" + sequi "follow" (see sequel). Pejorative sense of "fawning, sycophantic" had emerged by 1599 (implied in obsequiously).

observance --- c.1225, "act performed in accordance with prescribed usage," esp. a religious or ceremonial one," from O.Fr. observance, from L. observantia "act of keeping customs, attention," from observantem (nom. observans), prp. of observare (see observe). Observance is the attending to and carrying out of a duty or rule. Observation is watching, noticing. Observant is attested from 1608; in ref. to Judaism, from 1902.

observation --- 1382, from L. observationem (nom. observatio) "a watching over," from observatus, pp. of observare (see observe). Meaning "a remark in reference to something observed" first recorded 1593.

observatory --- 1676 (in ref. to Greenwich), from Fr. observatoire, from observer (v.), from O.Fr. (see observe).

observe --- c.1386, "to hold to" (a manner of life or course of conduct), from O.Fr. observer, from L. observare "watch over, look to, attend to, guard," from ob "over" + servare "to watch, keep safe," from PIE base *ser- "to protect." Meaning "to attend to in practice, to keep, follow" is attested from 1390. Sense of "watch, perceive, notice" is c.1560, via notion of "see and note omens." Meaning "to say by way of remark" is from 1605.

obsess --- 1503, "to besiege," from L. obsessus, pp. of obsidere "besiege, occupy," lit. "sit opposite to," from ob "against" + sedere "sit." Of evil spirits, "to haunt," is from 1540. Obsession was originally (1513) "the act of besieging," then "hostile action of the devil or an evil spirit" (1605); meaning "persistent influence or idea" is first recorded 1680. Obsessive (adj.) formed 1911. Obsessive-compulsive is attested from 1927.

obsidian --- 1656, from L. obsidianus, misprint of obsianus (lapis) "(stone) of Obsius," a Roman alleged by Pliny to have found this rock in Ethiopia.

obsolescent --- 1755, from L. obsolescentum (nom. obsolescens), prp. of obsolescere "fall into disuse" (see obsolete). Obsolescence is attested from 1828.

obsolete --- 1579, from L. obsoletus "grown old, worn out," pp. of obsolescere "fall into disuse," probably from ob "away" + solere "to be used to, be accustomed."

obstacle --- c.1340, from O.Fr. ostacle "hindrance," from L. obstaculum "a hindrance, obstacle," from obstare "stand opposite to, block, hinder," from ob "against" + stare "to stand," from PIE base *sta- "to stand" (see stet).

obstetrics --- 1819, from obstetric (adj.), 1742, from Mod.L. obstetricus "pertaining to a midwife," from obstetrix (gen. obstetricis) "midwife," lit. "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]

obstinate --- c.1340, from L. obstinatus "resolute, inflexible, stubborn," pp. of obstinare "persist, stand stubbornly, set one's mind on," from ob "by" + stinare, related to stare "stand," from PIE base *sta- "to stand" (see stet).

obstreperous --- 1600, from L. obstreperus "clamorous," from obstrepere "drown with noise, oppose noisily," from ob "against" + strepere "make a noise," from PIE *strep-, said to be imitative.

obstruction --- 1533, from L. obstructionem (nom. obstructio) "a building up," from obstructus, pp. of obstruere "block up, build up, hinder," from ob "against" + struere "to pile, build" (see structure). Obstruct is attested from 1611.

obtain --- c.1425, from M.Fr. obtenir (14c.), from L. obtinere "hold, take hold of, acquire," from ob "to" (though perhaps intensive in this case) + tenere "to hold" (see tenet).

obtrude --- c.1555, from L. obtrudere "thrust into, press upon," from ob "toward" + trudere "to thrust" (see extrusion).

obtuse --- 1509, from M.Fr. obtus (fem. obtuse), from L. obtusus "blunted, dull," pp. of obtundere "to beat against, make dull," from ob "against" + tundere "to beat," from PIE *(s)tud- "to beat, strike, push, thrust" (cf. L. tudes "hammer," Skt. tudati "he thrusts"). Sense of "stupid" is first found 1509. The verb obtund (trans.) "to render dead, make dull" has occasionally been used, esp. in medical jargon, since c.1400.

obverse --- 1656 (adj.), from L. obversus, pp. of obvertere "to turn toward or against," from ob "toward" + vertere "to turn" (see versus). The noun, in ref. to coins, medals, etc. (opposite of reverse), is attested from 1658.

obviate --- 1598, "to meet and do away with," from L.L. obviatus, pp. of obviare "act contrary to, go against," from L. obvius "that is in the way, that moves against" (see obvious).

obvious --- 1586, "frequently met with," from L. obvius "that is in the way, presenting itself readily, commonplace," from obviam (adv.) "in the way," from ob "against" + viam, acc. of via "way." Meaning "plain to see, evident" is first recorded 1635.

ocarina --- 1877, from It. ocarina, dim. of oca "goose" (so called for its shape), from V.L. *auca, from L. avicula "small bird," dim. of avis "bird" (see aviary).

Occam's razor --- when two competing hypotheses explain the data equally well, choose the simpler. Named for Eng. philosopher William of Ockham (c.1285-c.1349).

occasion (n.) --- 1382, from O.Fr. occasion, from L. occasionem (nom. occasio) "opportunity, appropriate time," from occasum, pp. of occidere "fall down, go down," from ob "down, away" + cadere "to fall" (see case (1)). The notion is of a "falling together," or juncture, of circumstances. The verb is first attested 1530. Occasional (1631) was originally "happening on some particular occasion;" sense of "happening as occasion presents itself, without regularity" is from 1630.

occident --- c.1375, from O.Fr. occident (12c.), from L. occidentem (nom. occidens) "western sky, part of the sky in which the sun sets," originally "setting" (adj.), prp. of occidere "fall down, go down" (see occasion).

occipital --- 1541, from M.Fr. occipital, from M.L. occipitalis, from L. occiput (gen. occipitis) "back of the skull," from ob "against, behind" + caput "head" (see head).

Occitian --- Old Provençal, langue d'Oc, 1940, also "the northern variant of modern Provençal."

occlude --- 1597, from L. occludere (pp. occlusus) "shut up, close up," from ob "against, up" + claudere "to shut, close" (see close (v.)). Of teeth, 1880 (implied in occlusion).

occult --- 1533, "secret, not divulged," from L. occultus "hidden, concealed, secret," pp. of occulere "cover over, conceal," from ob "over" + a verb related to celare "to hide," from PIE base *kel- (see cell). Meaning "not apprehended by the mind, beyond the range of understanding" is from 1545. The association with the supernatural sciences (magic, alchemy, astrology, etc.) dates from 1633.

occupant --- 1596, from L. occupantem (nom. occupans), prp. of occupare "to take possession of" (see occupy).

occupation --- c.1340, "a being employed in something," also "a particular action," from O.Fr. occupacion (12c.), from L. occupationem (nom. occupatio) "a taking possession, business, employment," from occupatus, pp. of from occupare (see occupy). Meaning "trade" is from 1530.

occupy --- c.1340, "to take possession of," also "to take up space or time, employ (someone)," from O.Fr. occuper, from L. occupare "take over, seize, possess, occupy," from ob "over" + intensive form of capere "to grasp, seize" (see capable). During 16c.-17c. a euphemism for "have sexual intercourse with," which caused it to fall from polite usage.

occur --- 1527, "meet, meet in argument," from M.Fr. occurrer, from L. occurrere "run to meet, run against, befall, present itself," from ob "against, toward" + currere "to run" (see current). 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 1626.

ocean --- c.1290, from O.Fr. occean (12c.), from L. oceanus, from Gk. okeanos, the great river or sea surrounding the disk of the Earth (as opposed to the Mediterranean), of unknown origin. Personified as Oceanus, son of Uranus and Gaia and husband of Tethys. 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 L. mare oceanum. Application to individual bodies of water began 14c.; there are usually reckoned to be five of them, but this is arbitrary; also occasionally applied to smaller subdivisions, e.g. German Ocean "North Sea." Oceanography coined in Eng. 1859, from Gk. graphia, from graphein "to write" (about).

Oceania --- southern Pacific island and Australia, conceived as a continent, 1849, Mod.L., from Fr. Océanie (c.1812). Apparently coined by Dan. geographer Conrad Malte-Brun (1755-1826). Earlier in Eng. as Oceanica (1832).

ocelot --- large wildcat of Central and South America, 1775, from Fr. ocelot, formed in Fr. by naturalist de Buffon (1707-1788), from Nahuatl ocelotl "jaguar" (in full tlalocelotl, a compound formed with tlalli "field").

ochlocracy --- government by the rabble, 1584, from Fr. ochlocratie (1568), from Gk. okhlokratia, from okhlos "mob" + kratos "rule, power, strength" (see -cracy).

ochre --- 1398, "type of clayey soil (much used in pigments)," from O.Fr. ocre (1307), from L. ochra, from Gk. ochra, from ochros "pale yellow," of unknown origin. As a color name, "brownish-yellow," it is attested from c.1440.

o'clock --- c.1720, abbreviation of of the clock, from M.E. of the clokke (1389). Attested from 1904 in ref. to direction (by shooters, fighter pilots, etc.).

octa- --- prefix meaning "eight," from L. octo, Gk. okto-, cognate with Skt. asta, Goth. ahtau, O.E. eahta (see eight).

octagon --- 1656, from L. octagonos, from Gk. oktagononos, lit. "eight-angled," from okta- comb. form of okto "eight" (see eight) + gonia "angle," related to gony "knee" (see knee). The adjective octagonal is attested from 1571.

octane --- hydrocarbon of the methane series, 1872, coined from octo- (from Gk. okto "eight;" see eight) + -ane, as in methane; so called because it has eight carbon atoms. A fuel's octane rating, in ref. to its anti-knocking quality, is attested from 1932.

octant --- instrument for making angular measurements in navigation or astronomy, 1731, from L.L. octans, from octo "eight" (see octa-).

octave --- c.1300, vtaues (pl., from popular O.Fr. form otaves), later reformed, from M.L. octava, from L. octava dies "eighth day," fem. of octavus "eighth," from octo (see eight). Originally "period of eight days after a festival," also "eighth day after a festival" (counting both days, thus if the festival was on a Sunday, the octaves would be the following Sunday). Verse sense of "stanza of eight lines" is from c.1586; musical sense of "note eight diatonic degrees above (or below) a given note" is first recorded 1656, from L. octava (pars) "eighth part."

Octavia --- fem. proper name, from L., fem. of Octavius, lit. "the eighth."

octavo --- 1582, printer's word for sheets folded to make eight leaves, from L. in octavo "in the eighth," from octavus "eighth" (see octave). Abbreviation is 8vo.

octo- --- see octa-.

October --- c.1050, from L. October (mensis), from octo "eight," from PIE base *octo(u)- "eight." For -ber see December. Replaced O.E. winterfylleð. In Rus. history, October Revolution (in which the Bolsheviks overthrew the Provisional Government) happened Nov. 7, but because Russia had not at that time adpoted the Gregorian calendar reform, this date was reckoned there (Old Style) as Oct. 25. Octobrist can have two senses: the first (from Rus. oktyabrist) is a member of the league formed October 1905 in response to imperial policies; the second (from Rus. Oktyabryonok) is a member of a Rus. communist children's organization, founded 1925 and named in honor of the October Revolution.