oft (adv.) Look up oft at Dictionary.com
Old English oft "often, frequently," from Proto-Germanic *ofta- "frequently" (cognates: Old Frisian ofta, Danish ofte, Old High German ofto, German oft, Old Norse opt, Gothic ufta "often"), of unknown origin. Archaic except in compounds (such as oft-told), and replaced by its derivative often.
often (adv.) Look up often at Dictionary.com
c.1300, extended form of oft, originally before vowels and h-, probably by influence of Middle English selden "seldom." In common use from 16c., replacing oft.
oftentimes Look up oftentimes at Dictionary.com
extended form of often, attested from early 15c.
ogee (n.) Look up ogee at Dictionary.com
"S-shaped molding," 1670s, from French ogive "diagonal rib of a vault," earlier augive, of unknown origin. Related: ogival.
ogham (n.) Look up ogham at Dictionary.com
also ogam, ancient Irish form of writing, 1620s, from Irish ogham, from Old Irish ogam, said to be from name of its inventor, Ogma Mac Eladan. But this appears to be from Celt. *Ogmios, perhaps from PIE *og-mo- "furrow, track," thus metaphorically "incised line." This could be the source of the name of the writing style, which looks like a series of cuts or incised lines, and the inventor's name thus might be folk etymology. Related: Oghamic.
ogle (v.) Look up ogle at Dictionary.com
1680s, probably from Low German oeglen, frequentative of oegen "look at," from oege "eye," from Proto-Germanic *augon-, from PIE *okw- "to see" (see eye (n.)). Related to Dutch ogen "to look at," from oog "eye." Related: Ogled; ogling. The noun meaning "an amorous glance" is attested from 1711; earlier it meant "an eye" (1700).
ogre (n.) Look up ogre at Dictionary.com
"man-eating giant," 1713, hogre (in a translation of a French version of the Arabian Nights), from French ogre, first used in Perrault's "Contes," 1697, and perhaps formed by him from Italian orco "demon, monster," from Latin Orcus "Hades," perhaps via an Italian dialect. In English, more literary than colloquial. The conjecture that it is from Byzantine Ogur "Hungarian" or some other version of that people's name (perhaps via confusion with the bloodthirsty Huns), lacks historical evidence. Related: Ogrish; ogrishness.
Ogygian (adj.) Look up Ogygian at Dictionary.com
1843, "of great antiquity or age," from Greek Ogygos, name of a mythical Attic or Boeotian king who even in classical times was thought to have lived very long ago. Also sometimes with reference to a famous flood said to have occurred in his day.
oh Look up oh at Dictionary.com
1530s, interjection expressing various emotions, a common Indo-European word (Old French ô;, oh; Latin o, oh; Greek o; Old Church Slavonic and Lithuanian o; Gothic, Dutch, German o; Old Irish a; Sanskrit a), but not found in Old English, which translated Latin oh with la or eala.
The present tendency is to restrict oh to places where it has a certain independence, & prefer o where it is proclitic or leans forward upon what follows .... [Fowler]
Often extended for emphasis, as in Oh, baby, stock saying from c.1918; oh, boy (1910); oh, yeah (1924). Reduplicated form oh-oh as an expression of alarm or dismay is attested from 1944. Oh-so "so very" (often sarcastic or ironic) is from 1922. Oh yeah? "really? Is that so?" attested from 1930.
Ohio Look up Ohio at Dictionary.com
originally used of the river, from Seneca (Iroquoian) ohi:yo', proper name from ohi:yo:h, literally "good river." The Seneca also used this of the Allegheny, which they considered the headwaters of the Ohio. Related: Ohian (1819); Ohioan (1818).
ohm (n.) Look up ohm at Dictionary.com
unit of electrical resistance, 1867, in recognition of German physicist Georg S. Ohm (1789-1854), who determined the law of the flow of electricity. Originally proposed as ohma (1861) as a unit of voltage. Related: ohmage; ohmic; ohmeter.
oho (interj.) Look up oho at Dictionary.com
14c., from oh + ho.
oi Look up oi at Dictionary.com
1962, vulgar or working class pronunciation of hoy a call or shout to attract attention.
oil (n.) Look up oil at Dictionary.com
late 12c., "olive oil," from Anglo-French and Old North French olie, from Old French oile, uile "oil" (12c., Modern French huile), from Latin oleum "oil, olive oil" (source of Spanish, Italian olio), from Greek elaion "olive tree," from elaia (see olive). Old English æle, Dutch olie, German Öl, etc. all are from Latin. It meant "olive oil" exclusively till c.1300, when meaning began to be extended to any fatty, greasy substance. Use for "petroleum" first recorded 1520s, but not common until 19c. The artist's oils (1660s), short for oil-color (1530s), are paints made by grinding pigment in oil.
oil (v.) Look up oil at Dictionary.com
mid-15c., from oil (n.). Related: Oiled; oiling. An Old English verb in this sense was besmyrian.
oilcloth (n.) Look up oilcloth at Dictionary.com
1690s, "cotton or a similar fabric waterproofed with oil," from oil (n.) + cloth. In reference to an oil-treated canvas used as a cheap floor covering, 1796.
oily (adj.) Look up oily at Dictionary.com
1520s, from oil (n.) + -y (2). Figurative meaning "smooth, unctuous" is from 1590s. Related: Oiliness.
oink (v.) Look up oink at Dictionary.com
"to make a noise like a pig," 1965, of imitative origin.
ointment (n.) Look up ointment at Dictionary.com
late 13c., from Old French oignement "ointment, salve, unguent," from Vulgar Latin *unguimentum, from Latin unguentum (see unguent). The first -t- emerged in Old French from oint, past participle of verb oindre "to anoint."
OJ Look up OJ at Dictionary.com
slang abbreviation of orange juice, attested by 1963.
Ojibwa Look up Ojibwa at Dictionary.com
Algonquian people of North America living along the shores of Lake Superior, 1700, from Ojibwa O'chepe'wag "plaited shoes," in reference to their puckered moccasins, which were unlike those of neighboring tribes. The older form in English is Chippewa, which is usually retained in U.S., but since c.1850 Canadian English has taken up the more phonetically correct Ojibwa, and as a result the two forms of the word have begun to be used in reference to slightly differing groups in the two countries. Some modern Chippewas prefer anishinaabe, which means "original people."
OK Look up OK at Dictionary.com
1839, only survivor of a slang fad in Boston and New York c.1838-9 for abbreviations of common phrases with deliberate, jocular misspellings (such as K.G. for "no go," as if spelled "know go;" N.C. for "'nuff ced;" K.Y. for "know yuse"). In the case of O.K., the abbreviation is of "oll korrect."

Probably further popularized by use as an election slogan by the O.K. Club, New York boosters of Democratic president Martin Van Buren's 1840 re-election bid, in allusion to his nickname Old Kinderhook, from his birth in the N.Y. village of Kinderhook. Van Buren lost, the word stuck, in part because it filled a need for a quick way to write an approval on a document, bill, etc. Spelled out as okeh, 1919, by Woodrow Wilson, on assumption that it represented Choctaw okeh "it is so" (a theory which lacks historical documentation); this was ousted quickly by okay after the appearance of that form in 1929. Greek immigrants to America who returned home early 20c. having picked up U.S. speech mannerisms were known in Greece as okay-boys, among other things.

The noun is first attested 1841; the verb 1888. Okey-doke is student slang first attested 1932.
okapi (n.) Look up okapi at Dictionary.com
short-necked giraffe of central Africa, 1900, from the animal's name in Mbuba (Congo). Reported by English explorer Sir Harry Johnston (1858-1927).
okay Look up okay at Dictionary.com
see OK.
oke Look up oke at Dictionary.com
slang clipping of OK, attested from 1929.
Okie Look up Okie at Dictionary.com
"migrant agricultural worker," especially one driven from farms in Oklahoma during the Dust Bowl, 1938, short for U.S. state of Oklahoma.
"Okie use' ta mean you was from Oklahoma. Now it means you're a dirty son-of-a-bitch." [John Steinbeck, "The Grapes of Wrath," 1939]
Okinawa Look up Okinawa at Dictionary.com
largest of the Ryuku island chain, Japanese, literally "rope on the sea." Related: Okinawan.
Oklahoma Look up Oklahoma at Dictionary.com
from Choctaw, literally "red people," from okla "nation, people" + homma "red." Coined by Choctaw scholar Allen Wright, later principal chief of the Choctaw Nation, and first used in the Choctaw-Chickasaw treaty of April 28, 1866. Organized as a U.S. territory 1889; admitted as a state 1907. Related: Oklahoman.
okra (n.) Look up okra at Dictionary.com
1670s, from a West African language (compare Akan nkruma "okra").
Olaf Look up Olaf at Dictionary.com
masc. proper name, from Old Norse An-leifr, literally "ancestor's relic;" first element related to Old High German ano "ancestor;" second element related to Old English læfan "to leave" (see leave (v.)).
Olbers' paradox Look up Olbers' paradox at Dictionary.com
"if stars are uniformly distributed through the sky, their number should counterbalance their faintness and the night sky should be as bright as the day;" named for German astronomer H.W.M. Olbers (1758-1840), who propounded it in 1826.
old (adj.) Look up old at Dictionary.com
Old English ald (Anglian), eald (West Saxon) "aged, antique, primeval; elder, experienced," from Proto-Germanic *althas "grown up, adult" (cognates: Old Frisian ald, Gothic alþeis, Dutch oud, German alt), originally a past participle stem of a verb meaning "grow, nourish" (compare Gothic alan "to grow up," Old Norse ala "to nourish"), from PIE root *al- (3) "to grow, nourish" (cognates: Greek aldaino "make grow, strengthen," althein, althainein "to get well;" Latin alere "to feed, nourish, bring up, increase," altus "high," literally "grown tall," almus "nurturing, nourishing," alumnus "fosterling, step-child;" Old Irish alim "I nourish").

The usual PIE root is *sen- (see senior (adj.)). A few Indo-European languages distinguish words for "old" (vs. young) from words for "old" (vs. new), and some have separate words for aged persons as opposed to old things. Latin senex was used of aged living things, mostly persons, while vetus (literally "having many years") was used of inanimate things. Greek geraios was used mostly of humans; Greek palaios was used mostly of things, of persons only in a derogatory sense. Greek also had arkhaios, literally "belonging to the beginning," which parallels French ancien, used mostly with reference to things "of former times."

Old English also had fyrn "ancient," related to Old English feor "far, distant" (see far, and compare Gothic fairneis, Old Norse forn "old, of old, of former times," Old High German firni "old, experienced"). The original Old English vowel is preserved in Scots auld, also in alderman. The original comparative and superlative (elder, eldest) are retained in particular uses.

First record of old-timer is from 1860. Expression old as the hills first recorded 1819. The good old days dates from 1828. Of old "of old times" is from late 14c. Old Glory for "the American flag" is first attested 1862. Old maid "woman who remains single well beyond the usual marrying age" is from 1520s; the card game is attested by that name from 1844. Old man "man who has lived long" is from c.1200; sense of "husband, father, boss" is from 1854, earlier (1830) it was military slang for "commanding officer;" old lady "wife, mother" is attested from c.1775. Old English is attested from 1701, originally as a type of font. Old boy originally was a former pupil of one of the English public schools. Old Testament attested from mid-14c.
old hat (adj.) Look up old hat at Dictionary.com
"out of date," first recorded 1911. As a noun phrase, however, it had different sense previously. The "Classical Dictionary of the Vulgar Tongue" (1796) defines it as, "a woman's privities, because frequently felt."
Old World (adj.) Look up Old World at Dictionary.com
of or pertaining to Eurasia and Africa, as opposed to the Americas, 1877.
old-fashioned (adj.) Look up old-fashioned at Dictionary.com
1590s, "in an outdated style," from old + past participle of fashion (v.). As a type of cocktail, attested from 1901, American English.
Old Fashioned Tom Gin Cocktail Mix same as Holland Gin Old Fashioned Cocktail using Old Tom gin in place of Holland [George J. Kappeler, "Modern American Drinks," Akron, Ohio, 1900]
old-school (adj.) Look up old-school at Dictionary.com
in reference to a group of people noted for conservative views or principles on some professional or political matter, 1749, from old + school (n.).
old-time (adj.) Look up old-time at Dictionary.com
1824, from old + time (n.). Related: Old-timey (1850).
olde Look up olde at Dictionary.com
pseudo-archaic mock-antique variant of old, 1927.
olden (adj.) Look up olden at Dictionary.com
early 15c., from old + -en (2).
oldie (n.) Look up oldie at Dictionary.com
"an old person," 1874; "an old tune or film," 1940, from old + -ie. Related: Oldies, which is attested by 1961 as a radio format.
oldness (n.) Look up oldness at Dictionary.com
Old English ealdnysse; see old + -ness.
oldster (n.) Look up oldster at Dictionary.com
1818, colloquial, from old + -ster, on analogy of youngster.
ole Look up ole at Dictionary.com
1922, from Spanish olé "bravo!"
oleaginous (adj.) Look up oleaginous at Dictionary.com
1630s, from French oléagineux (14c.), from Latin oleaginus "of the olive," from olea "olive," alteration of oliva (see olive) by influence of oleum "oil."
oleander (n.) Look up oleander at Dictionary.com
"rose bay," a poisonous evergreen Mediterranean shrub, c.1400, from Medieval Latin oleander, probably (by influence of Latin olea "olive tree") from Late Latin lorandrum, from Latin rhododendron (see rhododendron), itself altered by influence of Latin laurea "laurel," on resemblance of leaves. This round-about etymology is supported by the French word for it, laurier rose.
Oleg Look up Oleg at Dictionary.com
masc. proper name; see Olga.
oleo (n.) Look up oleo at Dictionary.com
1884, commercial shortening of oleomargarine.
oleo- Look up oleo- at Dictionary.com
word-forming element meaning "oil" or "oleic," from Latin oleum (see oil (n.)).
oleomargarine (n.) Look up oleomargarine at Dictionary.com
1873, "butter substitute made from beef fat," from French oléomargarine (1854), from oléine (from Latin oleum "oil" + -ine, after glycerine) + margarine. It was regarded as a chemical compound of olein and margarine.
olfaction (n.) Look up olfaction at Dictionary.com
noun of action from Latin olfactus, past participle of olfacere "to smell, get the smell of" (transitive), from olere "to emit a smell" (see odor) + facere "to make" (see factitious).