Online Etymology Dictionary

osteopath (n.): 1897, back-formation from osteopathy.
osteopathy (n.): 1857, "disease of the bones," from Greek osteon "bone" (see osseous) + -pathy, from Greek -patheia, comb. form of pathos "suffering, disease, feeling" (see pathos). As a system of treating ailments by the manipulation of bones, it dates from 1889.
osteoporosis (n.): 1846, from osteo- + stem of Greek poros "passage, pore, voyage" (see pore (n.)) + -osis. Related: Osteoporotic.
ostinato: 1876, from Italian ostinato, literally "obstinate, persistent."
ostler (n.): late 14c., phonetic spelling of hostler.
ostomy (n.): 1957, abstracted from colostomy, etc.; ultimately from Modern Latin stoma "opening, orifice," from Greek stoma "mouth" (see stoma).
ostracise (v.): chiefly British English spelling of ostracize (q.v.); for suffix, see -ize. Related: Ostracised.
ostracism (n.): 1580s, a method of 10-year banishment in ancient Athens, by which the citizens gathered and each wrote on a potsherd or tile the name of a man they deemed dangerous to the liberties of the people, and a man whose name turned up often enough was sent away. From Middle French ostracisme (16c.), Modern Latin ostracismus, or directly from Greek ostrakismos, from ostrakizein "to ostracize," from ostrakon "tile, potsherd," from PIE *ost-r-, from root *ost- "bone" (see osseous). The Greek word is related to osteon "bone," ostreion "oyster" (and cognate with German Estrich "pavement," which is from Medieval Latin astracus "pavement," ultimately from Greek ostrakon).

A similar practice in ancient Syracuse (with banishment for five years) was by writing names on olive leaves, and thus was called petalismos.
ostracize (v.): 1640s, from Greek ostrakizein "to banish," literally "to banish by voting with potshards" (see ostracism). Figurative sense of "to exclude from society" is attested from 1640s. Related: Ostracization; ostracized; ostracizing.
ostrich (n.): early 13c., from Old French ostruce "ostrich" (Modern French autruche) and Medieval Latin ostrica, ostrigius, all from Vulgar Latin avis struthio, from Latin avis "bird" (see aviary) + Late Latin struthio "ostrich," from Greek strouthion "ostrich," from strouthos megale "big sparrow," perhaps from PIE *trozdo- "thrush" (see thrush (n.1)). The Greeks also knew the bird as strouthokamelos "camel-sparrow," for its long neck. Among its proverbial peculiarities are indiscriminate voracity (especially a habit of swallowing iron and stone to aid digestion), want of regard for its eggs, and a tendency to hide its head in the sand when pursued.
Like the Austridge, who hiding her little head, supposeth her great body obscured. [1623, recorded in OED]
Ostriches do put their heads in the sand, but ostrich farmers say they do this in search of something to eat.
Ostrogoth (n.): c.1600, one of the "East Goths," who conquered Italy late 5c. and established, under Theodric, a kingdom there that lasted from 493 to 555 C.E., from Late Latin Ostrogothæ, from Germanic, literally "eastern Goths" from Proto-Germanic *aust(a)r- "east" (see east; for second element, see Goth; also cf. Visigoth), but according to Klein this is a folk corruption of an earlier Austrogoti, from a Germanic compound, the first element of which means "shining" or "splendid," from Proto-Germanic *austr-, from PIE *ausr- (see aurora), which is also, via "sunrise," the root of the Latin word for "east."
Oswald: masc. proper name, from Old English Osweald "god-power, god-ruler," from Old English os "god" (only in personal names), from PIE *ansu- "spirit" (see Oscar) + Old English (ge)weald "power."
otalgia (n.): 1650s, from Greek otalgia "earache," from ous, aus (genitive otos) "ear" (see ear (n.1)) + algos "pain" (see -algia).
other (adj.): Old English oþer "the second" (adj.), also as a pronoun, "one of the two, other," from Proto-Germanic *antharaz (cf. Old Saxon athar, Old Frisian other, Old Norse annarr, Middle Dutch and Dutch ander, Old High German andar, German ander, Gothic anþar "other").

These are from PIE *an-tero-, variant of *al-tero- "the other of two" (cf. Lithuanian antras, Sanskrit antarah "other, foreign," Latin alter), from root *al- "beyond" (see alias) + adjectival comparative suffix *-tero-. The Old English, Old Saxon, and Old Frisian forms show "a normal loss of n before fricatives" [Barnhart]. Meaning "different" is mid-13c.

Sense of "second" was detached from this word in English (which uses second, from Latin) and German (zweiter, from zwei "two") to avoid ambiguity. In Scandinavian, however, the second floor is still the "other" floor (e.g. Swedish andra, Danish anden). Also cf. Old English oþergeara "next year."

The other woman "a woman with whom a man begins a love affair while he is already committed" is from 1855. The other day originally (mid-12c.) was "the next day;" later (c.1300) "yesterday;" and now, loosely, "a day or two ago" (early 15c.). Phrase other half in reference to either the poor or the rich, is recorded from c.1600.
La moitié du monde ne sçayt comment l'aultre vit. [Rabelais, "Pantagruel," 1532]
otherness (n.): 1580s, from other + -ness.
otherwise (adv.): contracted from Old English phrase on oðre wisan "in the other manner" (see other + wise (n.)), which in Middle English became oþre wise, and mid-14c. oþerwise. As an adjective from c.1400.
otherworldly (adj.): 1854, from other + world + -ly (1). Otherworldliness is recorded from 1819. Phrase other world "world of idealism or fantasy, afterlife, spirit-land" is c.1200.
otic (adj.): "pertaining to the ear," from Greek otikos, from ous (genitive otos) "ear" (see ear (n.1)).
otiose (adj.): 1794, "unfruitful, futile," from Latin otiosus "having leisure or ease,unoccupied, idle, not busy" (source of French oiseux, Spanish ocioso, Italian otioso), from otium "leisure, free time, freedom from business," of unknown origin. Meaning "at leisure, idle" is recorded from 1850. Cf. Latin phrase otium cum dignitate "leisure with dignity." Earlier adjective in English was otious- "at ease" (1610s), and Middle English had noun otiosity (late 15c.).
ottava rima: 1820, Italian, "eight-lined stanza," literally "eighth rhyme," from ottava "eighth" (see octave). A stanza of eight 11-syllable lines, rhymed a b a b a b c c, but in the Byronic variety, they are English heroic lines of 10 syllables.
Ottawa: Canadian capital, founded 1827 as Bytown, named for English officer John By, who oversaw construction of the canal there; renamed 1854, when it became capital, for the Ottawa River, which took its name from the Algonquian people who lived in Michigan and Ontario. Their name is said to be from adawe "to trade."
otter (n.): Old English otr, otor "otter," from Proto-Germanic *otraz (cf. Old Norse otr, Swedish utter, Danish odder, Dutch otter, Old High German ottar, German Otter), from PIE *udros, literally "water-creature" (cf. Sanskrit udrah, Avestan udra "otter;" Greek hydra "water-serpent," enydris "otter;" Latin lutra, Old Church Slavonic vydra, Lithuanian udra, Old Irish odoirne "otter"), from root *wed- "water" (see water (n.1)).
Ottoman: 1580s (n.), c.1600 (adj.), from French Ottoman, from Italian Ottomano, from Arabic 'Uthmani "of or belonging to 'Uthman," Arabic masc. proper name, which in Turkish is pronounced Othman (see Osmanli), name of the founder of the dynasty and empire. Ending altered in Italian by formation of a new false singular, because -i was a plural inflection in Italian. Byron used the more correct form Othman, and a few writers have followed him. The type of couch so called (1806) because one reclined on it, which was associated with Eastern customs (see couch).
oubliette (n.): "secret dungeon reached only via trapdoor," 1819, from French oubliette (14c.), from Middle French oublier "to forget, show negligence," Old French oblier, oblider, from Vulgar Latin *oblitare, from Latin oblitus, past participle of oblivisci "to forget" (see oblivion).
ouch: 1837, from Pennsylvania German outch, cry of pain, from German autsch. The Japanese word is itai. Latin used au, hau.
oud (n.): "lute or mandolin of Arab lands," 1738, from Arabic 'ud, literally "wood." Also cf. lute.
ought (v.): Old English ahte "owned, possessed," past tense of agan "to own, possess, owe" (see owe). As a past tense of owe, it shared in that word's evolution and meant at times in Middle English "possessed" and "under obligation to pay." It has been detached from owe since 17c., though he aught me ten pounds is recorded as active in East Anglian dialect from c.1825. As an auxiliary verb expressing duty or obligation (late 12c., the main modern use), it represents the past subjunctive.
ought (n.): "zero, cipher," 1844, probably a misdivision of a nought (see nought; for misdivision, see N); meaning probably influenced by aught "anything."
Ouija: 1891, a trademark name (originally by Kennard Novelty Co., Baltimore, Md.), compounded from French oui + German ja, both meaning "yes."
ounce (n.1): unit of weight, early 14c., from Old French once, unce, a measure of weight or time (12c.), from Latin uncia "one-twelfth part" (of a pound, foot, etc.), from Latin unus "one" (see one). The Latin word had been adopted in Old English as ynce (see inch). It was one-twelfth of a pound in the Troy system of weights, but one-sixteenth in avoirdupois. Abbreviation oz. is from older Italian onza. Also used in Middle English as a measure of time (7.5 seconds) and length (about 3 inches).
ounce (n.2): "wildcat," c.1300, from Old French once "lynx" (13c.), from lonce, with l- mistaken as definite article, from Vulgar Latin *luncea, from Latin lyncea "lynx-like," from lynx (see lynx). Originally the common lynx, later extended to other wildcats, now mainly used of the mountain-panther or snow leopard of Asia.
our (pron.): Old English ure "of us," genitive plural of the first person pronoun, from Proto-Germanic *ons (cf. Old Saxon usa, Old Frisian use, Old High German unsar, German unser, Gothic unsar "our"), from PIE *nes-, oblique case of personal pronoun in first person plural (cf. Latin nos "we," noster "our"). Also cf. ours. Ourselves (late 15c.), modeled on yourselves, replaced original construction we selfe, us selfum, etc.
ours: c.1300, a double possessive (with genitive suffix -s (1)), originating in northern England, and has taken over the absolute function of our (q.v.). In Middle English ourn, ouren also were used.
oust (v.): early 15c., from Anglo-French oster (late 13c.), Old French oster "remove, take away, take off; evict, dispel; liberate, release" (Modern French ôter), from Latin obstare "stand before, be opposite, stand opposite to, block," in Vulgar Latin, "hinder," from ob "against" (see ob-) + stare "to stand," from PIE root *sta- "to stand" (see stet). Related: Ousted; ousting.
ouster (n.): "ejection from property," 1530s, noun use of Anglo-French ouster (see oust). For other such usages, see waiver.
out (adv.): Old English ut "out, without, outside," common Germanic (cf. Old Norse, Old Frisian, Old Saxon, Gothic ut, Middle Dutch uut, Dutch uit, Old High German uz, German aus), from PIE root *ud- "up, out, up away" (cf. Sanskrit ut "up, out," uttarah "higher, upper, later, northern;" Avestan uz- "up, out," Old Irish ud- "out," Latin usque "all the way to, without interruption," Greek hysteros "the latter," Russian vy- "out"). Meaning "into public notice" is from 1540s. As an adjective from c.1200. Meaning "unconscious" is attested from 1898, originally in boxing. Sense of "not popular or modern" is from 1966. As a preposition from mid-13c.

Sense in baseball (1860) was earlier in cricket (1746). Adverbial phrase out-and-out "thoroughly" is attested from early 14c.; adjective usage is attested from 1813; out-of-the-way (adj.) "remote, secluded" is attested from late 15c. Out-of-towner "one not from a certain place" is from 1911. Shakespeare's It out-herods Herod ("Hamlet") reflects Herod as stock braggart and bully in old religious drama and was widely imitated 19c. Out to lunch "insane" is student slang from 1955; out of this world "excellent" is from 1938; out of sight "excellent, superior" is from 1891.
out (v.): Old English utian "expel, put out" (see out (adv.)); used in many senses over the years. Meaning "to expose as a closet homosexual" is first recorded 1990 (as an adjective meaning "openly avowing one's homosexuality" it dates from 1970s; see closet); sense of "disclose to public view, reveal, make known" has been present since mid-14c.
Eufrosyne preyde Þat god schulde not outen hire to nowiht. [Legendary of St. Euphrosyne, c.1350]
Related: Outed; outing.
out (n.): 1620s, "a being out" (of something), from out (adv.). From 1860 in baseball sense; from 1919 as "means of escape; alibi."
out-bid (v.): 1580s, from out (adv.) + bid (v.). Related: Out-bidding; out-bidden.
out-building (n.): "a detached or subordinate building," 1620s, from out + building (n.).
out-take (n.): "rejected part of a film," 1960, from out + take (n.) in the movie sense.
out-thrust (adj.): 1820, from out (adv.) + thrust (v.).
outage (n.): "period or condition in which electrical power is disconnected," 1903, American English; formed from out on model of shortage.
outback (n.): "back-country, interior regions of Australia," 1907, Australian English, originally an adverb, "out in the back settlements" (1878), from out + back (adv.).
outboard (adj.): "situated on the outside of a ship," 1823, from out + board (n.2). In reference to motors, from 1909.
outbreak (n.): "eruption" (of disease, hostilities, etc.), c.1600, from out + break (v.). Outbreak was a verb in Middle English (c.1300).
outburst (n.): 1650s, from out + burst (v.). Outbresten was a verb in Middle English (mid-12c.), from Old English utaberstan.
outcast (n.): mid-14c., "a person cast out or rejected," originally past participle of Middle English outcasten, from out + casten "to cast" (see cast (v.)). The adjective is attested from late 14c. In an Indian context, outcaste "one who has been expelled from his caste" is from 1876; see caste.
outclass (v.): 1870, "to beat (a rival) so completely as to put him out of the same class," from out + class (v.).
outcome (n.): 1788, "that which results from something," originally Scottish, from out + come (v.). Popularized in English by Carlyle (c.1830s). Used in Middle English in sense of "act or fact of coming out" (c.1200). Old English had utancumen (n.) "stranger, foreigner."