Online Etymology Dictionary

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."
octogenarian (n.): 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 *dekm- "ten" (see ten). As an adjective from 1784.
octopod: 1826 (adj.); 1835 (n.), from Latinized form of Greek oktopod-, from stem of oktopous (see octopus).
octopus (n.): 1758, genus name of a type of eight-armed cephalopod mollusks, from Greek oktopous, literally "eight-footed," from okto "eight" (see eight) + pous "foot" (see foot (n.)). Proper plural is octopodes, though octopuses probably works better in English. Octopi is from mistaken assumption that -us in this word is the Latin noun ending that takes -i in plural.
octoroon (n.): 1861, irregular formation from Latin octo "eight" (see eight) + suffix abstracted from quadroon (in which the suffix actually is -oon). Offspring of a quadroon and a white; so called for having one-eighth Negro blood.
octuple (adj.): "eightfold," c.1600, from Latin octuplus "eightfgold," from octo "eight" (see octo-) + -plus "-fold" (see plus).
ocular (adj.): c.1500, from Late Latin ocularis "of the eyes," from Latin oculus "an eye," from PIE root *okw- "to see" (cf. Gothic augo, Old English eage "eye;" see eye (n.)). As a noun, 1835, from the adjective.
oculist (n.): "eye doctor," 1610s, from French oculiste (16c.), from Latin oculus "an eye" (see eye (n.)).
oculus: "an eye," plural oculi, 1857, from Latin oculus "an eye" (see eye (n.)).
oda (n.): room in a harem, 1620s, from Turkish odah "hall, chamber."
odalisque (n.): "female slave in a harem," 1680s, from French odalisque (1660s), from Turk. odaliq "maidservant," from odah "room in a harem," literally "chamber, hall," + -liq, suffix expressing function. In French, the suffix was confused with Greek -isk(os) "of the nature of, belonging to."
odd (adj.): c.1300, "constituting a unit in excess of an even number," from Old Norse oddi "third or additional number," as in odda-maðr "third man, odd man (who gives the casting vote)," odda-tala "odd number." The literal meaning of Old Norse oddi is "point of land, angle" (related via notion of "triangle" to oddr "point of a weapon"); from Proto-Germanic *uzdaz "pointed upward" (cf. Old English ord "point of a weapon, spear, source, beginning," Old Frisian ord "point, place," Dutch oord "place, region," Old High German ort "point, angle," German Ort "place"), from PIE *uzdho- (cf. Lithuanian us-nis "thistle"). None of the other languages, however, shows the Old Norse development from "point" to "third number." Used from late 14c. to indicate a surplus over any given sum.

Sense of "strange, peculiar" first attested 1580s from notion of "odd one out, unpaired one of three" (attested earlier, c.1400, as "singular" in a positive sense of "renowned, rare, choice"). Odd job (c.1770) is so called from notion of "not regular." Odd lot "incomplete or random set" is from 1897. The international order of Odd Fellows began as local social clubs in England, late 18c., with Masonic-type trappings; formally organized 1813 in Manchester.
oddball (n.): "eccentric or unconventional person," 1948, from odd + ball (n.1). Earlier (1946) as an adjective, used by aviators.
odditorium (n.): 1914, from oddity + -orium (see -ory).
oddity (n.): 1713, "odd characteristic or trait," a hybrid from odd + -ity. Meaning "odd person" is first recorded 1748.
oddly (adv.): c.1300, from odd + -ly (2).
oddments (n.): 1780, a hybrid with a Latin suffix on a Germanic word, from odd (q.v.), on model of fragments. Related: Oddment.
oddness (n.): late 14c., from odd + -ness.
odds (n.): in wagering sense, found first in Shakespeare ("2 Henry IV," 1597), probably from earlier sense of "amount by which one thing exceeds or falls short of another" (1540s), from odd (q.v.), though the sense evolution is uncertain. Until 19c. treated as a singular, though obviously a plural (cf. news).
ode (n.): 1580s, from Middle French ode (c.1500), from Late Latin ode "lyric song," from Greek oide, Attic contraction of aoide "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.
odeon (n.): 1902, from Greek oideion "building for musical performance."
odeum (n.): "concert hall," c.1600, from Latin odeum, from Greek odeion, the name of a public building in Athens designed for musical performances, from oide "song" (see ode).
odiferous (adj.): c.1500, odeferus, "fragrant," shortened variant of odoriferous. Related: Odiferously; odiferousness.
Odin: chief Teutonic god, the All-Father, a 19c. revival in reference to Scandinavian neo-paganism, from Danish, from Old Norse Oðinn, from Proto-Germanic *Wod-enaz- (source of Old English Woden, Old High German Wuotan), probably from *wod-eno-/*wod-ono- "raging, mad, inspired," from root *wet- "to blow, inspire, spiritually arouse" (see wood (adj.)).
odious (adj.): late 14c., from Anglo-French odious, from Old French odieus (late 14c., Modern French odieux) or directly from Latin odiosus "hateful, offensive, unpleasant," from odium "hatred" (see odium).
odium (n.): c.1600, "fact of being hated," from Latin odium "ill-will, hatred, grudge, animosity; offense, offensive conduct," related to odi "I hate" (infinitive odisse), from PIE root *od- "to hate" (cf. Armenian ateam "I hate," Old Norse atall, Old English atol "dire, horrid, loathsome"). Meaning "hatred, detestation" is from 1650s. Often in an extended form, e.g. odium theologicum "hatred which is proverbially characteristic of theological disputes" (1670s).
odometer (n.): 1791, from French odomètre (1724), from Greek hodos "way" (see cede) + -meter. First recorded in writings of Thomas Jefferson.
odor (n.): c.1300, from Anglo-French odour, from Old French odor "smell, perfume, fragrance" (12c., Modern French odeur) and directly from Latin odor "a smell, a scent" (pleasant or disagreeable), from PIE *od- "to smell" (cf. Latin olere "emit a smell, to smell of," with Sabine -l- for -d-; Greek ozein "to smell;" Armenian hotim "I smell;" Lithuanian uodziu "to smell").

Good or bad odor, in reference to repute, estimation, is from 1835. Odor of sanctity (1756) is from French odeur de sainteté (17c.) "sweet or balsamic scent said to be exhaled by the bodies of eminent saints at death or upon disinterment."
odoriferous (adj.): early 15c., "that has a scent," with -ous + Latin odorifer "spreading odor, fragrant," literally "bearing odor," from odor (see odor) + ferre "to bear, carry" (see infer). Usually in a positive sense.
odorous (adj.): "fragrant," early 15c., from Medieval Latin odorosus, from Latin odorus "having a smell," from odor (see odor).
odour (n.): chiefly British English spelling of odor (q.v.); for spelling, see -or.
Odysseus: king of Ithaca, from Greek Odysseus (Latin Ulysses), of unknown origin, perhaps related to odyssasthai "to be grieved at, be angry at."
odyssey (n.): c.1600, "Odyssey," from Latin Odyssea, from Greek Odysseia, name of the Homeric epic poem of ancient Greece, relating the ten-year wanderings of Odysseus, king of Ithaca, after the Trojan War. Figurative sense of "long, adventurous journey" is first recorded 1889.
oe: found in Greek borrowings into Latin, representing Greek -oi-. Words with -oe- that came early into English from Old French or Medieval Latin usually already had been levelled to -e- (e.g. economic, penal, cemetery), but later borrowings directly from Latin or Greek tended to retain it at first (oestrus, diarrhoea, amoeba) as did proper names (Oedipus, Phoebe, Phoenix) and purely technical terms. British English tends to be more conservative with it than American, which has done away with it in all but a few instances.

It also occurred in some native Latin words (foedus "treaty, league," foetere "to stink," hence occasionally in English foetid, foederal, which was the form in the original publications of the "Federalist" papers). In these it represents an ancient -oi- in Old Latin (e.g. Old Latin oino, Classical Latin unus), which apparently passed through an -oe- form before being levelled out but was preserved into Classical Latin in certain words, especially those belonging to the realms of law (e.g. foedus) and religion, which, along with the vocabulary of sailors, are the most conservative branches of any language in any time, through a need for precision, immediate comprehension, demonstration of learning, or superstition. But in foetus it was an unetymological spelling in Latin that was picked up in English and formed the predominant spelling of fetus into the early 20c.
OED: initialism of Oxford English Dictionary, attested from 1898, according to the "Oxford English Dictionary."
Oedipal (adj.): 1939, "of or pertaining to desire felt for opposite-sex parent," from Oedipus complex (1910), coined by Freud from Sophocles' play "Oedipus Tyrannus," in which the title character, the Theban hero, answers the Sphinx's riddle and unknowingly kills his father and marries his own mother; from Greek Oedipus. The name was used figuratively in English from 1550s for "one who is clever at guessing riddles," which had adjectival form Oedipean (1620s).
Oedipus: son of Laius and Jocasta, the king and queen of Thebes, Greek, literally "swollen-foot," from oidan "to swell" (from PIE *oid-; see edema) + pous (genitive podos) "foot" (see foot (n.)). Oedipus complex (1910) coined by Freud. In Latin, figurative references to Oedipus generally referred to solving riddles. Oedipus effect (1957) is Karl Popper's term for "the self-fulfilling nature of prophecies or predictions."
oeillade (n.): "an oogling stare, an amorous gaze," 1590s, from French oeillide (15c.), from oeil "eye" (from Latin oculus, see eye (n.)) + -ade.
oeno-: also oino-, word-forming element meaning "pertaining to wine," from comb. form of Greek oinos "wine" (see wine (n.)).
oenology (n.): 1827, from oeno- "wine" + -logy. Related: Oenological; oenologist.
oenophile (n.): 1930 (as an adjective 1900), probably from French oenophile, from Greek oinos "wine" (see wine) + -phile.
oesophagus (n.): alternative spelling of esophagus. See oe. Related: Oesophageal.
oestrogen (n.): see estrogen.
oestrus (n.): see estrus.
oeuvre (n.): "a work," especially a work of literature, also "the body of work produced by an artist," 1875, from French oeuvre "work" (12c.), from Latin opera (see opus).
of (prep.): Old English of, unstressed form of æf (prep., adv.) "away, away from," from Proto-Germanic *af (cf. Old Norse af, Old Frisian af, of "of," Dutch af "off, down," German ab "off, from, down"), from PIE *apo- "off, away" (see apo-). Primary sense in Old English still was "away," but shifted in Middle English with use of the word to translate Latin de, ex, and especially Old French de, which had come to be the substitute for the genitive case. "Of shares with another word of the same length, as, the evil glory of being accessory to more crimes against grammar than any other." [Fowler]

Also from 1837 a non-standard or dialectal representation of have as pronounced in unstressed positions (could of, must of, etc.)
of-: assimilated form of ob- before -f-.
ofay (n.): American English black slang, "white person," 1925, of unknown origin. If, as is sometimes claimed, it derives from an African word, none corresponding to it has been found. Perhaps the most plausible speculation is Yoruba ófé "to disappear" (as from a powerful enemy), with the sense transferred from the word of self-protection to the source of the threat. OED regards the main alternative theory, that it is pig Latin for foe, to be no more than an "implausible guess."
off (adv.): by c.1200 as an emphatic form of Old English of (see of), employed in the adverbial use of that word. The prepositional meaning "away from" and the adjectival sense of "farther" were not firmly fixed in this variant until 17c., but once they were they left the original of with the transferred and weakened senses of the word. Meaning "not working" is from 1861. Off the cuff (1938) is from the notion of speaking from notes written in haste on one's shirt cuffs. Off the rack (adj.) is from 1963; off the record is from 1933; off the wall "crazy" is 1968, probably from the notion of a lunatic "bouncing off the walls" or else in reference to carom shots in squash, handball, etc.
off (v.): "to kill," 1930, from off (adv.). Earlier verbal senses were "to defer" (1640s), "to move off" (1882). Related: Offed.