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Online Etymology Dictionary
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Q Look up Q at Dictionary.com
16th letter of the classical Roman alphabet, from the Phoenician equivalent of Heb. koph, which was used for the more guttural of the two "k" sounds in Semitic. The letter existed in Greek, but was little used and not alphabetized; the stereotypical connection with -u- began in Latin. Anglo-Saxon scribes adopted the habit at first, but later used spellings with cw- or cu-. The qu- pattern returned to English with the Norman Conquest. Scholars use -q- alone to transliterate Semitic koph (e.g. Quran, Qatar, Iraq). In Christian theology, Q has been used since 1901 to signify the hypothetical source of passages shared by Matthew and Luke, but not in Mark; probably it is an abbreviation of Ger. Quelle "source."
Q and A Look up Q and A at Dictionary.com
also Q & A, 1954, abbreviation of question and answer (itself attested by 1817).
Q.E.D. Look up Q.E.D. at Dictionary.com
1760, abbreviation of L. quod erat demonstrandum "which was to be demonstrated."
q.t. Look up q.t. at Dictionary.com
slang for "quiet," in on the q.t., attested from 1874. Phrase on the quiet appears from 1847.
qi (n.) Look up qi at Dictionary.com
"physical life force," 1850, from Chinese qi "air, breath."
qua Look up qua at Dictionary.com
"as, in the capacity of," from L. qua, ablative singular fem. of qui "who," from PIE *kwo-, stem of relative and interrogative pronouns (cf. O.E. hwa "who," hwæt "what;" Goth. hvas "who;" Gk. posos "how much?").
quaalude (n.) Look up quaalude at Dictionary.com
1965, proprietary name (trademark by Wm. H. Rohrer Inc., Ft. Washington, Pennsylvania, U.S.A.) of methaqualone.
quab (n.) Look up quab at Dictionary.com
"sea-slug," 1610s, from M.Du. or M.L.G. quabbe (Du. kwab).
quack (v.) Look up quack at Dictionary.com
"to make a duck sound," 1610s, quelke, of echoic origin (cf. M.Du. quacken, O.C.S. kvakati, L. coaxare "to croak," Gk. koax "the croaking of frogs," Hitt. akuwakuwash "frog"). M.E. on the quakke (14c.) meant "hoarse, croaking." Related: Quacked; quacking.
quack (n.) Look up quack at Dictionary.com
"medical charlatan," 1630s, short for quacksalver (1570s), from Du. kwaksalver, lit. "hawker of salve," from M.Du. quacken "to brag, boast," lit. "to croak" (see quack (v.)) + zalf "salve" (see salve (v.)). Cf. Ger. Quacksalber, Dan. kvaksalver, Swed. kvacksalvare.
quackery (n.) Look up quackery at Dictionary.com
c.1710, from quack (n.) + -ery.
quad Look up quad at Dictionary.com
1820 as a shortening of quadrangle; 1896 as quadruplet; 1970 as quadraphonic. Related: Quads.
quadrangle (n.) Look up quadrangle at Dictionary.com
late 14c., from O.Fr. quadrangle (13c.), from L.L. quadrangulum "four-sided figure," properly neuter of Latin adjective quadrangulus "having four quarters," from L. quattuor "four" (see four) + angulus "angle" (see angle (n.)). The shortened form quad for "quadrangle of a college," is first recorded 1820 in Oxford slang.
quadrangular (adj.) Look up quadrangular at Dictionary.com
early 15c., from M.L. quadrangularis, from L.L. quadrangulum (see quadrangle).
quadrant (n.) Look up quadrant at Dictionary.com
late 14c., "a quarter of a day, six hours," from L. quadrantem (nom. quadrans) "fourth part," noun use of prp. of quadrare "to make square," from quadrus "a square," from quattuor "four" (see four). The surveying instrument is first so called c.1400, because it forms a quarter circle.
quadraphonic (adj.) Look up quadraphonic at Dictionary.com
1969, irregular formation from quadri- "four" + phonic, from Gk. phone "sound, voice" (see fame). The goal was to reproduce front-to-back sound distribution in addition to side-to-side stereo.
quadratic (adj.) Look up quadratic at Dictionary.com
1650s, "square," from quadrate (late 14c.), from L. quadratus "square," pp. of quadrare "to square," related to quattuor "four" (see four). Quadratic equations (1660s) so called because they involve the square of x.
quadrennial (adj.) Look up quadrennial at Dictionary.com
1650s, "lasting four years;" as "happening every four years," 1701; from quadri- + ending from biennial, etc. Correct formation would be *quadriennial Related: Quadrennially.
quadri- Look up quadri- at Dictionary.com
before vowels quad-, comb. form meaning “four, four times,” from L. quadri-, related to quattor “four” (see four).
quadricep (n.) Look up quadricep at Dictionary.com
1840, from quadri- on model of bicep. Related: Quadriceps.
quadrilateral (n.) Look up quadrilateral at Dictionary.com
1650, from L. quadrilaterus, from quadri- "four" (see quadri-) + latus (gen. lateris) "side" (see oblate (n.)).
quadrille (n.) Look up quadrille at Dictionary.com
1773, "lively square dance for four couples," from Fr. quadrille, originally one of four groups of horsemen in a tournament (a sense attested in English from 1738), from Sp. cuadrilla, dim. of cuadro "four-sided battle square," from L. quadrum "a square," related to quattuor "four" (see four). The craze for the dance hit England in 1816, and it underwent a vigorous revival late 19c. among the middle classes. Earlier a popular card game for four hands (1726).
Quadrille began to take the place of ombre as the fashionable card game about 1726, and was in turn superseded by whist. [OED]
quadrillion (n.) Look up quadrillion at Dictionary.com
1670s, from Fr. quadrillion (16c.) from quadri- "four" (see quadri-) + (m)illion. Cf. billion. In Great Britain, the fourth power of a million (1 followed by 24 zeroes); in the U.S., the fifth power of a thousand (1 followed by 15 zeroes).
quadriplegia (n.) Look up quadriplegia at Dictionary.com
1895, from quadri- + ending from paraplegia.
quadriplegic (adj.) Look up quadriplegic at Dictionary.com
also quadraplegic, 1897, a medical hybrid coined from Latin-based quadri- "four" + -plegic, as in paraplegic; ultimately from Gk. plege "stroke," from root of plessein "to strike" (see plague). A correct, all-Greek formation would be *tessaraplegic. The noun is first attested 1912, from the adjective.
quadroon (n.) Look up quadroon at Dictionary.com
1707, "offspring of a white and a mulatto," from Sp. cuarteron (used chiefly of the offspring of a European and a mestizo), from cuarto "fourth," from L. quartus (see quart), so called because he or she has one quarter African blood. Altered by influence of words in quadr-.
quadruped (n.) Look up quadruped at Dictionary.com
1610s (implied in quadrupedal), from Fr. quadrupède, from M.Fr., from L. quadrupes (gen. quadrupedis) "four-footed, a four-footed animal," from quadri- "four" (see quadri-) + pes "foot" (see foot). The adjective is attested from 1741.
quadruple (v.) Look up quadruple at Dictionary.com
late 14c., from L. quadruplare "make fourfold," from quadruplus (n.) "quadruple," from quadri- "four" (see quadri-) + -plus "fold."
quadruplet (n.) Look up quadruplet at Dictionary.com
"one of four children at a single birth," 1787; see quadruple. Related: Quadruplets. Musical sense is from 1873.
quaere Look up quaere at Dictionary.com
Latin imperative of quaerere "to ask, inquire" (see query). Hence "one may ask" (1530s).
quaff (v.) Look up quaff at Dictionary.com
1510s (implied in quaffer), perhaps onomatopoeic, or perhaps from Low Ger. quassen "to overindulge (in food and drink)," with -ss- misread as -ff-. Related: Quaffed; quaffing. The noun is from 1570s.
quag (n.) Look up quag at Dictionary.com
"marshy spot," 1580s, a variant of M.E. quabbe "a marsh, bog," from O.E. *cwabba "shake, tremble" (like something soft and flabby).
quagga (n.) Look up quagga at Dictionary.com
1785, from Afrikaans (1710), from the name for the beast in a native language, perhaps Hottentot quacha, probably of imitative origin. In modern Xhosa, the form is iqwara, with a clicking -q-. The last one died in an Amsterdam zoo in 1883.
quagmire (n.) Look up quagmire at Dictionary.com
1570s, from obsolete quag "bog, marsh" + mire (n.). Extended sense of "difficult situation, inextricable position" is recorded by 1766.
quahog (n.) Look up quahog at Dictionary.com
1753, from an Algonquian language, perhaps Narragansett poquauhock or Pequot p'quaghhaug "hard clam."
quai (n.) Look up quai at Dictionary.com
1870, from Fr. quai (see quay). Often short for Quai D'Orsay, street on the south bank of the Seine in Paris, site of the French Ministry of Foreign Affairs and sometimes used metonymically for it (1922).
quail (n.) Look up quail at Dictionary.com
c.1300, quayle, from O.Fr. quaille, perhaps via M.L. quaccula (cf. Prov. calha, It. quaglia, O.Sp. coalla), from a Germanic source (cf. O.H.G. quahtala "quail," Ger. Wachtel), imitative of the bird's cry. Or the English word might be directly from Germanic. Slang meaning "young attractive woman" first recorded 1859.
quail (v.) Look up quail at Dictionary.com
"to lose heart, to shrink," c.1400, of unknown origin, perhaps from M.Du. quelen "to suffer, be ill," from P.Gmc. *kwel- "to die" (see quell). Or from obsolete quail "to curdle" (late 14c.), from O.Fr. coailler, from L. coagulare (see coagulate). Sense of "cower" is attested from 1550s. Common 1520-1650, then rare until 19c.; apparently revived by Scott. Related: Quailed; quailing.
quaint (adj.) Look up quaint at Dictionary.com
early 13c., "cunning, proud, ingenious," from O.Fr. cointe "pretty, clever, knowing," from L. cognitus "known," pp. of cognoscere "get or come to know well" (see cognizance). Sense of "old-fashioned but charming" is first attested 1795, and could describe the word itself, which had become rare after c.1700 (though it soon recovered popularity in this secondary sense). Chaucer used quaint and queynte as spellings of cunt in "Canterbury Tales" (c.1386), and Andrew Marvell may be punning on it similarly in "To His Coy Mistress" (1650).
quake (v.) Look up quake at Dictionary.com
O.E. cwacian "quake, tremble, chatter (of teeth)," related to cweccan "to shake, swing, move, vibrate," of unknown origin with no certain cognates outside English. Perhaps somehow imitative. Related: Quaked; quaking. The noun is attested from c.1400, originally "a trembling in fear," but was rare except in combinations.
Quaker (n.) Look up Quaker at Dictionary.com
1651, said to have been applied to them in 1650 by Justice Bennett at Derby, from George Fox's admonition to his followers to "tremble at the Word of the Lord;" but the word was used earlier of foreign sects given to fits of shaking during religious fervor, and that is likely the source here. Either way, it was never an official name of the Religious Society of Friends. The word in a literal sense is attested from early 15c. Quaker gun (1809, American English) was a log painted black and propped up to look from a distance like a cannon, so called for the sect's noted pacifism.
quale (n.) Look up quale at Dictionary.com
"death, destruction," O.E. cwalu, cognate with O.N. kval "torment, torture," from a variant of the root of quell.
qualification (n.) Look up qualification at Dictionary.com
1540s, "restriction, modification," from M.L. qualificationem (nom. qualificatio), noun of action from pp. stem of qualificare (see qualify). Meaning "accomplishment that qualifies someone to do something" is from 1660s; that of "necessary precondition" is from 1723. Related: Qualifications.
qualifier (n.) Look up qualifier at Dictionary.com
1560s, agent noun from qualify. Grammatical sense is from 1580s.
qualify (v.) Look up qualify at Dictionary.com
mid-15c., "to invest with a quality," from M.L. qualificare "attribute a quality to," from L. qualis "of what sort" (see quality) + facere "to make" (see factitious). Sense of "be fit for a job" first appeared 1580s. Related: Qualified; qualifying.
qualitative (adj.) Look up qualitative at Dictionary.com
early 15c., from L.L. qualitativus, from L. qualitas (see quality). Related: Qualitatively.
quality (n.) Look up quality at Dictionary.com
c.1300, "temperament, character, disposition," from O.Fr. qualite (12c., Mod.Fr. qualité), from L. qualitatem (nom. qualitas; said to have been coined by Cicero to translate Gk. poiotes), from qualis "of what sort," from PIE pronomial base *kwo- (see qua). Meaning "degree of goodness" is late 14c. Meaning "social rank, position" is c.1400. Noun phrase quality time first recorded 1977. Quality of life is from 1943. Quality control first attested 1935.
qualm (n.) Look up qualm at Dictionary.com
O.E. cwealm (W.Saxon) "death, disaster, plague," utcualm (Anglian) "utter destruction," related to cwellan "to kill," cwelan "to die" (see quell). Sense softened to "feeling of faintness" 1520s; meaning "uneasiness, doubt" is from 1550s; that of "scruple of conscience" is 1640s.

A direct connection between the Old English and modern senses is wanting, but it is nonetheless plausible, via the notion of "fit of sickness." The other suggested etymology, less satisfying, is from Du. kwalm "steam, vapor, mist," which also may be ultimately from the same Germanic root as quell.
qualms (n.) Look up qualms at Dictionary.com
see qualm.
quandary (n.) Look up quandary at Dictionary.com
1570s, "state of perplexity," of unknown origin, perhaps a quasi-Latinism based on L. quando "when."