Online Etymology Dictionary

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 *Wodanaz, name of the chief Germanic god (source of Old English Woden, Old High German Wuotan), from PIE *wod-eno-, *wod-ono- "raging, mad, inspired," from root *wet- (1) "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" (source also of Armenian ateam "I hate," Old Norse atall, Old English atol "dire, horrid, loathsome"). Meaning "hatred, detestation" is from 1650s. Often in an extended form, such as 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" (source also of 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- (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 (for example Old Latin oino, Classical Latin unus), which apparently passed through an -oe- form before being leveled out but was preserved into Classical Latin in certain words, especially those belonging to the realms of law (such as 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 (acronym) 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," from PIE root *ped- (1) "a 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 (n.)) + -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 (source also of 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.): African-American vernacular, "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." Sometimes shortened to fay (1927).
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.
off-and-on (adv.): "intermittently," 1530s; see off (adv.) + on. As an adjective from 1580s.
off-base (adv.): "unawares," 1936, American English, from off (adv.) + base (n.); a figurative extension from baseball sense of "not in the right position" (1898), from notion of a baserunner being picked off while taking a lead.
off-beat (adj.): also offbeat, "unusual," 1938, from off (adv.) + beat (n.). From earlier sense in reference to from music rhythm (1927).
off-Broadway (adj.): 1953, "experimental theater productions in New York City," from off (adv.) + Broadway. Even more experimental off-off-Broadway is attested from 1967.
off-camera (adj.): 1944, from off (adv.) + camera.
off-chance (n.): 1861, from off (adv.) + chance (n.).
off-color (adj.): 1858, from off (adv.) + color (n.); originally used of gems; figurative extension to "of questionable taste, risqué" is American English, 1867.
off-colour (adj.): see off-color.
off-duty (adj.): 1743, from off (adv.) + duty.
off-hand (adv.): also offhand, 1690s, "at once, straightway," from off (adv.) + hand (n.). Probably originally in reference to shooting without a rest or support. Hence, of speech or action, "unpremeditated" (1719). Related: Off-handed; off-handedly.
off-key (adj.): 1920, from off (adv.) + musical sense of key (n.1). Figurative sense is from 1943.
off-limits (adj.): "forbidden," by 1881, U.S. military academies jargon, from off (adv.) + limit (n.). Earlier (1857) it was applied to cadets, etc., who were in violation of the limitations on their movement and behavior.
off-line (adj.): 1926, of railroads; 1950, of computers; from off (adv.) + line (n.).
off-load (v.): "unload," 1850, from off (adv.) + load (v.). Originally S.African, on model of Dutch afladen.
off-peak (adj.): 1906, originally in reference to electrical systems, from off (adv.) + peak (n.).
off-putting: 1570s, "procrastinating," from off (adv.) + put (v.). Meaning "creating an unfavorable impression" is first recorded 1894.
off-ramp (n.): 1954, from off (adv.) + ramp (n.).
off-road (adj.): 1949, from off (adv.) + road.
off-season (n.): 1848, "a period when business is down," from off (adv.) + season (n.).
off-shore (adj.): also off shore, 1720, from off + shore (n.). American English use for "other than the U.S." is from 1948 and the Marshall Plan.