Online Etymology Dictionary

-oholic: abstracted from alcoholic (q.v.).
-oid: suffix for "like, like that of," from Gk. -oeides, from eidos "form," related to idein "to see," eidenai "to know;" lit. "to see," from PIE *weid-es-, from base *weid- "to see, to know" (see vision).
-ol: chemical suffix, variously representing alcohol, phenol, or in some cases L. oleum “oil.”
-ola: commercial suffix, probably originally in pianola (q.v.).
-ology: suffix indicating "branch of knowledge, science," the usual form of -logy, with the -o- belonging to the preceding element.
-oma: from Gk. -oma, from -ma, suffix forming neuter nouns; especially taken in medical use as "marked growth, tumor."
-on: subatomic particle suffix, from ion.
-or: suffix forming nouns of quality, state, or condition, from M.E. -our, from O.Fr. -our (Fr. -eur), from L. -orem (nom. -or), a suffix added to pp. verbal stems. Also in some cases from L. -atorem (nom. -ator). In U.S., via Noah Webster, -or is nearly universal (but not in glamour, curious, generous), while in Britain -our is used in most cases (but with many exceptions: author, error, senator, ancestor, horror etc.). The -our form predominated after c.1300, but Mencken reports that the first three folios of Shakespeare's plays used both spellings indiscriminately and with equal frequency; only in the Fourth Folio of 1685 does -our become consistent. A partial revival of -or on the L. model took place from 16c. (governour began to lose its -u- 16c. and it was gone by 19c.), and also among phonetic spellers in both England and America (John Wesley wrote that -or was "a fashionable impropriety" in England in 1791). In the U.S., Noah Webster criticized the habit of deleting -u- in -our words in his first speller ("A Grammatical Institute of the English Language," commonly called the Blue-Black Speller) in 1783. His own deletion of the -u- began with the revision of 1804, and was enshrined in the influential "Comprehensive Dictionary of the English Language" (1806), which also established in the U.S. -ic for British -ick and -er for -re, along with many other attempts at reformed spelling which never caught on (e.g. masheen for machine). His attempt to justify them on the grounds of etymology and the custom of great writers does not hold up. Fowler notes the British drop the -u- when forming adjs. ending in -orous (humorous) and derivatives in -ation and -ize, in which cases the Latin origin is respected (e.g. vaporize). When the Americans began to consistently spell it one way, the British hardened their insistence on the other. "The American abolition of -our in such words as honour and favour has probably retarded rather than quickened English progress in the same direction." [Fowler]
-osis: suffix expressing state or condition, in medical terminology denoting "a state of disease," from L. -osis, from Gk. -osis, formed from the aorist of verbs ending in -o. It corresponds to L. -atio.
-our: see -or.
-ous: suffix forming adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from O.Fr. -ous, -eux, from L. -osus.
o: interj. of fear, surprise, admiration, etc., see oh.
O: blood type, 1926, originally "zero," denoting absence of A and B agglutinogens.
O': as a prefix in Irish names, from Ir. ó, ua (O.Ir. au) "descendant."
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.).
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.
"That wilfull and vnruly age, which lacketh rypenes and discretion, and (as wee saye) hath not sowed all theyr wyeld Oates." [Thomas Newton, "Lemnie's Touchstone of complexions," 1576]
Hence, to feel (one's) oats "be lively," 1831, originally Amer.Eng.
oater: Western film, "horse opera," 1951, from oat.
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).
obduracy: 1590s, from obdurate.
obdurate: mid-15c., 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."
obedience: in reference to dog training is attested from 1930; from L. obedientia, from obediens (see obedient).
obedient: early 13c., from O.Fr. obedient (11c.), from L. obedientem (nom. obediens), prp. of oboedire "to obey" (see obey).
obeisance: late 14c., "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.
obese: 1650s, from L. obesus, pp. of obedere (see obesity).
obesity: 1610s, 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).
obey: late 13c., 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: late 14c., "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.): late 14c., "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 late 14c. 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.)).
objectification: 1830s, from objectify.
objectify: 1830s, from M.L. objectum (see object (n.)). Related: Objectified.
objection: late 14c., 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: 1781, from objection + -able.