Online Etymology Dictionary

quag (n.): "marshy spot," 1580s, a variant of Middle English quabbe "a marsh, bog," from Old English *cwabba "shake, tremble" (like something soft and flabby).
quagga (n.): zebra-like South African animal, 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-. What was likely the last one died in an Amsterdam zoo in 1883.
quagmire (n.): 1570s, "bog, marsh," from obsolete quag "bog, marsh" + mire (n.). Early spellings include quamyre (1550s), quabmire (1590s), quadmire (c. 1600). Extended sense of "difficult situation, inescapable bad position" is recorded by 1766; but this seems to have been not in common use in much of 19c. (absent in "Century Dictionary," 1902), but revived in a narrower sense in reference to military invasions in American English, 1965, with reference to Vietnam (popularized in the book title "The Making of a Quagmire" by David Halberstam).
quahog (n.): 1753 (quogue; Roger Williams had it as poquauhock, 1643), from an Algonquian language, perhaps Narragansett poquauhock or Pequot p'quaghhaug "hard clam."
quai (n.): 1870, "public path beside a waterway," from French quai (12c., see quay). Often short for Quai d'Orsay, the street on the south bank of the Seine in Paris, since mid-19c. site of the French Ministry of Foreign Affairs and hence sometimes used metonymically for it (1922).
quail (n.): migratory game bird, late 14c. (early 14c. as a surname (Quayle), from Old French quaille (Modern French caille), perhaps via Medieval Latin quaccula (source also of Provençal calha, Italian quaglia, Old Spanish coalla), or directly from a Germanic source (compare Dutch kwakkel, Old High German quahtala "quail," German Wachtel, Old English wihtel), imitative of the bird's cry. Or the English word might be directly from Proto-Germanic. Slang meaning "young attractive woman" first recorded 1859.
quail (v.): c. 1400, "have a morbid craving;" early 15c., "grow feeble or sick;" mid-15c., "to fade, fail, give way," of unknown origin, perhaps from Middle Dutch quelen "to suffer, be ill," from Proto-Germanic *kwaljan, from PIE *gwele- (1) "to throw, to pierce" (see quell). Or from obsolete quail "to curdle" (late 14c.), from Old French coailler, from Latin coagulare (see coagulate). Sense of "lose heart, shrink, cower" is attested from 1550s. According to OED, common 1520-1650, then rare until 19c., when apparently it was revived by Scott. Related: Quailed; quailing.
quaint (adj.): c. 1200, cointe, "cunning, ingenious; proud," from Old French cointe "knowledgeable, well-informed; clever; arrogant, proud; elegant, gracious," from Latin cognitus "known, approved," past participle of cognoscere "get or come to know well" (see cognizance). Modern spelling is from early 14c.

Later in English, "elaborate, skillfully made" (c. 1300); "strange and clever" (mid-14c.). 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). Related: Quaintly; quaintness.
quake (v.): Old English 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. In reference to earth tremors, probably by c. 1200. Related: Quaked; quaking.
quake (n.): early 14c., "a trembling in fear," from quake (v.). Rare except in combinations. Now usually as a shortening of earthquake, in which use it is attested from 1640s. Old English had the verbal noun cwacung "shaking, trembling."
Quaker (n.): 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 never was an official name of the Religious Society of Friends. The word in a literal sense is attested from early 15c., an agent noun from quake (v.).
There is not a word in the Scripture, to put David's condition into rime and meeter: sometimes he quaked and trembled, and lay roaring all the day long, that he watered his bed with his tears: and how can you sing these conditions (but dishonour the Lord) and say all your bones quake, your flesh trembled, and that you water your bed with your tears? when you live in pride and haughtiness, and pleasure, and wantonness;" etc. ["A Brief Discovery of a threefold estate of Antichrist Now Extant in the world, etc.," an early Quaker work, London, 1653]
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. Philadelphia, Pennsylvania, has been known as the Quaker City since at least 1824. Related: Quakerish; Quakeress ("a female Quaker"); Quakerism.
quale (n.): "death, destruction," Old English cwalu, cognate with Old Norse kval "torment, torture," from a variant of the root of quell.
qualification (n.): 1540s, "restriction, modification," from Middle French qualification and directly from Medieval Latin qualificationem (nominative qualificatio), noun of action from past participle 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.): 1560s, agent noun from qualify. Grammatical sense is from 1580s.
qualify (v.): mid-15c., "to invest with a quality," from Middle French qualifier (15c.) and directly from Medieval Latin qualificare "attribute a quality to; make of a certain quality," from Latin qualis "of what sort?," correlative pronominal adjective (see quality) + facere "to make" (see factitious). Meaning "to limit, modify" is from 1530s. Sense of "be fit for a job" first appeared 1580s. Related: Qualified; qualifying.
qualitative (adj.): early 15c., "that produces a (physical) quality," from Medieval Latin qualitativus "relating to quality," from stem of Latin qualitas "a quality, property, nature" (see quality). Meaning "concerned with quality" is from c. 1600 in English, from French qualitatif or Medieval Latin qualitativus. Related: Qualitatively.
quality (n.): c. 1300, "temperament, character, disposition," from Old French qualite "quality, nature, characteristic" (12c., Modern French qualité), from Latin qualitatem (nominative qualitas) "a quality, property; nature, state, condition" (said [Tucker, etc.] to have been coined by Cicero to translate Greek poiotes), from qualis "what kind of a," from PIE pronominal base *kwo- (see who). 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.): Old English cwealm (West Saxon) "death, murder, slaughter; disaster; plague; torment," utcualm (Anglian) "utter destruction," probably related to cwellan "to kill, murder, execute," cwelan "to die" (see quell). Sense softened to "feeling of faintness" 1520s; figurative meaning "uneasiness, doubt" is from 1550s; that of "scruple of conscience" is 1640s.

Evidence of a direct path from the Old English to the modern senses is wanting, but it is plausible, via the notion of "fit of sickness." The other suggested etymology, less satisfying, is to take the "fit of uneasiness" sense from Dutch kwalm "steam, vapor, mist" (cognate with German Qualm "smoke, vapor, stupor"), which also might be ultimately from the same Germanic root as quell.
qualms (n.): see qualm.
quandary (n.): "state of perplexity," 1570s, of unknown origin, perhaps a quasi-Latinism based on Latin quando "when? at what time?; at the time that, inasmuch," pronominal adverb of time, related to qui "who" (see who). Originally accented on the second syllable.
quango (n.): 1973, acronym for quasi-non-governmental organization (a descriptive phrase itself attested from 1967). Related: Quangocracy; quangocrat.
quantifiable (adj.): 1868, from quantify + -able. Related: Quantifiably.
quantification (n.): 1850, noun of action from quantify.
quantify (v.): 1840, from Medieval Latin quantificare, from Latin quantus "as much," correlative pronominal adjective (see quantity) + facere "to make" (see factitious). Literal sense of "determine the quantity of, measure" is from 1878. Related: Quantified; quantifying.
quantitation (n.): 1952, from quantity + -ation. Related: Quantitate.
quantitative (adj.): 1580s, "having quantity," from Medieval Latin quantitativus, from stem of Latin quantitas (see quantity). Meaning "measurable" is from 1650s. Related: Quantitatively.
quantitive (adj.): 1650s, from quantity + -ive. Related: Quantitively.
quantity (n.): early 14c., from Old French quantite, cantite (12c., Modern French quantité) and directly from Latin quantitatem (nominative quantitas) "relative greatness or extent," coined as a loan-translation of Greek posotes (from posos "how great? how much?") from Latin quantus "of what size? how much? how great? what amount?," correlative pronominal adjective, related to qui "who" (see who). Latin quantitatem also is the source of Italian quantita, Spanish cantidad, Danish and Swedish kvantitet, German quantitat.
quantum (n.): 1610s, "one's share or portion," from Latin quantum (plural quanta) "as much as, so much as; how much? how far? how great an extent?" neuter singular of correlative pronominal adjective quantus "as much" (see quantity). Introduced in physics directly from Latin by Max Planck, 1900; reinforced by Einstein, 1905. Quantum theory is from 1912; quantum mechanics, 1922; quantum jump is first recorded 1954; quantum leap, 1963, often figurative.
quarantine (n.): 1520s, "period of 40 days in which a widow has the right to remain in her dead husband's house." Earlier quarentyne (15c.), "desert in which Christ fasted for 40 days," from Latin quadraginta "forty," related to quattuor "four" (see four).

Sense of "period a ship suspected of carrying disease is kept in isolation" is 1660s, from Italian quarantina giorni, literally "space of forty days," from quaranta "forty," from Latin quadraginta. So called from the Venetian custom of keeping ships from plague-stricken countries waiting off its port for 40 days (first enforced 1377) to assure that no latent cases were aboard. The extended sense of "any period of forced isolation" is from 1670s.
quarantine (v.): 1804, from quarantine (n.). Related: Quarantined; quarantining.
quark (n.): 1964, applied by U.S. physicist Murray Gell-Mann (b.1929), who said in correspondence with the editors of the OED in 1978 that he took it from a word in James Joyce's "Finnegans Wake" (1939), but also that the sound of the word was in his head before he encountered the printed form in Joyce. German Quark "curds, rubbish" has been proposed as the ultimate inspiration [Barnhart; Gell-Mann's parents were immigrants from Austria-Hungary]. George Zweig, Gell-Mann's co-proposer of the theory, is said to have preferred the name ace for them.
quarrel (n.1): "angry dispute," mid-14c., originally "ground for complaint," from Old French querele "matter, concern, business; dispute, controversy" (Modern French querelle), from Latin querella "complaint, accusation; lamentation," from queri "to complain, lament." Replaced Old English sacan. Sense of "contention between persons" is from 1570s.
quarrel (n.2): "square-headed bolt for a crossbow," mid-13c., from Old French quarel, carrel "bolt, arrow," from Vulgar Latin *quadrellus, diminutive of Late Latin quadrus (adj.) "square," related to quattuor "four" (see four). Now-archaic sense of "square or diamond-shaped plane of glass" first recorded mid-15c.
quarrel (v.): late 14c., "to raise an objection;" 1520s as "to contend violently, to fall out," from quarrel (n.1) and in part from Old French quereler (Modern French quereller). Related: Quarrelled; quarrelling.
quarrelsome (adj.): 1590s, from quarrel (n.1) + -some (1). Related: Quarrelsomeness.
quarry (n.1): "what is hunted," early 14c., quirre "entrails of deer placed on the hide and given to dogs of the chase as a reward," from Anglo-French quirreie, Old French cuiriee "the spoil, quarry" (Modern French curée), altered (by influence of Old French cuir "skin," from Latin corium "hide"), from Old French corée "viscera, entrails," from Vulgar Latin *corata "entrails," from Latin cor "heart," from PIE root *kerd- (1) "heart" (see heart (n.)). Sense of "anything chased in hunt" is first recorded 1610s; earlier "bird targeted by a hawk or other raptor" (late 15c.).
quarry (n.2): "open place where rocks are excavated," c. 1400 (mid-13c. as a place name), from Medieval Latin quareia, dissimilated from quarreria (mid-13c.), literally "place where stones are squared," from Latin quadrare "to square" (see quadrant).
quarry (v.): 1774, from quarry (n.2). Related: Quarried; quarrying.
quarryman (n.): 1610s, from quarry (n.2) + man (n.). Related: Quarrymen.
quart (n.): "one-fourth of a gallon," early 14c., from Old French quarte "a fourth part" (13c.), from Latin quarta (pars), from fem. of quartus "the fourth," related to quattuor "four," from PIE root *kewtwor- (see four). Compare Latin quartarius "fourth part," also the name of a small liquid measure (the fourth part of a sextarius), which was about the same as an English pint.
quarter (n.): c. 1300, "one-fourth of anything; one of four parts or divisions of a thing;" often in reference to the four parts into which a slaughtered animal is cut, from Old French quartier, cartier (12c.), from Latin quartarius "fourth part," from quartus "fourth" (see quart). One of the earliest dated references in English is to "parts of the body as dismembered during execution" (c. 1300).

Used of the phases of the moon from early 15c. The use of quarter of an hour is attested from mid-15c. In Middle English quarter also meant "one of the four divisions of a 12-hour night" (late 14c.), and the quarter of the night meant "nine o'clock p.m." (early 14c.).

From late 14c. as "one of the four quadrants of the heavens;" hence, from the notion of the winds, "a side, a direction" (c. 1400). In heraldry from mid-14c. as "one of the four divisions of a shield or coat of arms." The word's connection with "four" loosened in Middle English and by 15c. expressions such as six-quartered for "six-sided" are found. Meaning "region, locality, area, place" is from c. 1400. Meaning "portion of a town" (identified by the class or race of people who live there) is first attested 1520s. For military sense, see quarters. As a period of time in a football game, from 1911. Quarter horse, bred strong for racing on quarter-mile tracks, first recorded 1834.

The coin (one fourth of a dollar) is peculiar to U.S., first recorded 1783. But quarter could mean "a farthing" in Middle English (late 14c.), and compare British quadrant "a farthing" (c. 1600), and classical Latin quadrans, the name of a coin worth a quarter of an as (the basic unit of Roman currency).

Quarter days (mid-15c.), designated as days when rents were paid and contracts and leases began or expired, were, in England, Lady day (March 25), Midsummer day (June 24), Michaelmas day (Sept. 29), and Christmas day (Dec. 25); in Scotland, keeping closer to the pagan Celtic calendar, they were Candlemas (Feb. 2), Whitsunday (May 15), Lammas (Aug. 1), and Martinmas (Nov. 11). Quarter in the sense "period of three months; one of the four divisions of a year" is recorded from late 14c.
quarter (v.): "to cut in quarters, divide into four parts," mid-14c., from quarter (n.). Specifically as the word for a form of criminal punishment from late 14c. (Old English had slitcwealm "death by rending"). Related: Quartered; quartering. The meaning "to put up soldiers" is recorded from 1590s (see quarters).
quarterback (n.): in U.S. football, 1876, from quarter (n.) + back (n.); so called from his position on the field at the start of play, between the halfback and the center. As a verb from 1945. Figurative sense from 1952. Monday morning quarterback is 1932 (n.), 1972 (v.); originally pro football player slang for sportswriters (U.S. professional football games typically are played on Sundays).
quarterly (adv.): early 15c., from quarter (n.) + -ly (2). As an adjective from 1560s, from -ly (1). As a noun, from 1830, "a quarterly publication," from the adjective.
quartermaster (n.): early 15c., "subordinate officer of a ship," from French quartier-maître or directly from Dutch kwartier-meester; originally a ship's officer whose duties included stowing of the hold; later (c. 1600) an officer in charge of quarters and rations for troops. See quarters.
quarters (n.): "military dwelling place," 1590s, from quarter (n.) in sense of "portion of a town." As "part of an American plantation where the slaves live," from 1724. The military sense seems to be also the source of quartermaster and it might be behind the phrase give quarter "spare from immediate death" (1610s, often in the negative), on the notion of "provide a prisoner with shelter."
quarterstaff (n.): also quarter-staff, 1540s (quarter-stroke "stroke with a quarterstaff" is attested from early 15c.), stout pole, six to eight feet long (six-and-a-half sometimes is given as the standard length), tipped with iron, formerly a weapon used by the English peasantry. From staff (n.); the quarter is of uncertain signification. According to one theory, favored by fencing manuals, etc., it likely is in reference to operation of the weapon:
It was grasped by one hand in the middle, and by the other between the middle and the end. In the attack the latter hand shifted from one quarter of the staff to the other, giving the weapon a rapid circular motion, which brought the ends on the adversary at unexpected points. [Century Dictionary]
Linguists tend to prefer an explanation from woodcutting, perhaps a reference to a cut of lumber known as a quarter, but contemporary evidence is wanting for either conjecture.
quartet (n.): 1773, "musical composition for four instruments or voices," from French quartette, from Italian quartetto, diminutive of quarto "fourth," from Latin quartus "fourth" (see quart). Meaning "set of four singers or musical performers" is from 1814.
quartile (n.): c. 1500, originally in astronomy; see quartile (adj.). In statistics, from 1879.