Words related to quell
*gwelə-, also *gwel-, Proto-Indo-European root meaning "to throw, reach," with extended sense "to pierce."
It forms all or part of: anabolic; arbalest; astrobleme; ball (n.2) "dancing party;" ballad; ballet; ballista; ballistic; ballistics; belemnite; catabolism; devil; diabolical; discobolus; emblem; embolism; hyperbola; hyperbole; kill (v.); metabolism; palaver; parable; parabola; parley; parliament; parlor; parol; parole; problem; quell; quail (v.) "lose heart, shrink, cower;" symbol.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit apa-gurya "swinging," balbaliti "whirls, twirls;" Greek ballein "to throw, to throw so as to hit," also in a looser sense, "to put, place, lay," bole "a throw, beam, ray," belemnon "dart, javelin," belone "needle," ballizein "to dance;" Armenian kelem "I torture;" Old Church Slavonic zali "pain;" Lithuanian galas "end," gėla "agony," gelti "to sting."
c. 1400, "have a morbid craving;" early 15c., "grow feeble or sick, begin to die;" mid-15c., "to fade, fail, give way," probably from Middle Dutch quelen "to suffer, be ill," from Proto-Germanic *kwaljan (source also of Old Saxon quelan "to die," Old High German quelan "die," German quälen "suffer pain"), from PIE root *gwele- "to throw, reach," with extended sense "to pierce."
Or perhaps from obsolete quail "to curdle" (late 14c.), from Old French coailler, from Latin coagulare (see coagulate).
Sense of "lose heart or courage, shrink before a danger or difficulty, cower" is attested from 1550s. According to OED, the word was common 1520-1650, then rare until 19c., when apparently it was revived by Scott. Related: Quailed; quailing.
Middle English, from Old English cwealm, cwelm (West Saxon) "death, murder, slaughter; disaster; widespread death by plague, pestilence or illness affecting humans or livestock; torment," utcualm (Anglian) "utter destruction," probably related to cwellan "to kill, murder, execute," cwelan "to die" (see quell).
The sense softened to "feeling of faintness" (1520s); the figurative meaning "uneasiness, doubt" is from 1550s; that of "a scruple of conscience" is from 1640s.
Evidence of a direct path from the Old English and Middle English senses (now obsolete) to the modern senses is wanting (OED 2nd edition has them as separate entries), and the old word seems to have become rare after c. 1400. 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.