Once John Cowan suggested that I touch on the murky history of the noun qualm and try to shed light on it. To the extent that I can trust my database, this word, which is, naturally, featured in all dictionaries, hardly ever appears in the special scholarly literature. The OED online opens the entry on qualm with a long discussion, weighs arguments on its origin, but offers no definitive solution. Everybody, including Elmar Seebold, the editor of Kluge’s etymological dictionary of German, believes that the early history of qualm is “obscure.” In my opinion, the obscurity is considerably less impenetrable than it seems to most. Below I’ll risk saying what I think about the subject without any support of our best authorities, past or present.
The facts are as follows. Engl. qualm turned up in texts in the sixteenth century. It meant “a sudden fit, impulse, or pang of sickening, misgiving, despair; a fit or sudden access of some quality, principle, etc.; a sudden feeling or fit of faintness or sickness” (OED). The first sense is still alive. Nowadays, the plural occurs more often, as in qualms of conscience, she had no qualms about…, and the like. Even when, as happens in this case, an English word has an almost unquestionable Germanic etymology but surfaces so late, there is a good chance that it is a borrowing.
German Qualm means “(a thick) smoke, vapor,” but the first recorded sense was “daze, stupefaction.” It too appeared in texts only in the sixteenth century, and the same conclusion must be valid for it as for its English look-alike. German researchers are positive that the word came to their Standard from Low (northern) German, and we should agree with them. “(Thick) smoke” and “sickness, nausea” are not incompatible: the first can cause the second. “Stupefaction” must be a later sense, and it is close to “a sudden pang of sickness” found in English.
In Soest (Westphalia, northern Germany), qualm means “a great quantity” (for example, of birds). This was noticed by Ferdinand Holthausen, a native of Soest. A leading philologist for many decades, he briefly discussed the local form in a journal article and later cited all the relevant words in his etymological dictionary of Old English. He also recorded the dialectal verb quullern “to gush (out, forth),” perhaps a cognate of Old Engl. collen “swollen,” known only as the first element of two compounds. Quull-er-n is obviously allied to German quell-en “to pour, stream” (the noun Quelle means “spring, source”). It does not look like a daring hypothesis to reconstruct the initial meaning of this family of words as “a mass of water or vapor (smoke) rising to the surface.” This may explain the sense of dialectal qualm “a great quantity,” with its reference to a flock of birds in the air.
Specification came later: from “smoke” to “suffocating smoke” and even further, as in the related German noun Qual, to “torment, pain, agony.” Old Engl. cwellan “to kill,” a congener but not the etymon of kill, continues into the modern language, though with a weakened meaning, as quell “extinguish.” Qual and Qualm are cognate. “Torment” and “daze, stupefaction” are close; final -m in Qualm is a suffix well-attested in Old Germanic and causes no trouble. Old Engl. cwelm ~ cwealm, derived from the same root, meant “pain, pestilence.”
The question about the origin of qualm (or rather of its German etymon) would have been settled once and for all but for the existence of another word, namely Old High German twalm “thick vapor; stupefaction,” an unexpected twin of Qualm with a different initial consonant group. It is the relation of twalm and Qualm that is supposed to be the real crux. Twalm, which did not survive the Middle High German period, has an instructive Old English cognate: dwalma “chaos” (Engl. d regularly corresponds to German t, as in do [Old Engl. don] ~ tun; Old Saxon had dwalm). Stupefaction and stupidity figure prominently in both Old English and German, as follows from Old Engl. dol “foolish,” dwol “heretical,” dwola “error, heresy,” dwolian “go astray,” dwolman “one who is in error, heretic,” and several compounds like dwolgod “false god, idol.” Modern Engl. dull is a borrowing of the cognate Middle Low German dul. All those words are related to the verb dwell, from dwellan “go astray, lead astray, deceive.”
As we can see, Old English had cwellan “kill” and dwellan “deceive.” Two German nouns correspond to them: Qualm (recorded late but, most probably, old) and twalm (an old word, now extinct). The groups—dwellan ~ dwalm ~ twalm and cwellan ~ qualm—are not related. But in scholarship some questions tend to live a dull, almost heretical life of their own. In a few German words, one of them being Quark, sometimes loosely glossed as “curds, cottage cheese” but often left untranslated, kw- arose by the change tw- to kw-, and the question haunts researchers whether qualm could also be the product of that sound change. Perhaps it could, but Occam’s razor exists expressly for such cases and advises us not to multiply moves unless necessary: the fewer superfluous assumptions are made, the better. Since we have a convincing derivation of qualm, why raise the ghost of its going back to twalm? Let us grant each of those words its independent existence. To be sure, two such nouns, which sounded alike and often had similar meanings, could interact, but, since this process cannot be observed or reconstructed, it need not bother us.
Here then is my summary. From the root cwell- (or kwell-) “gush forth” the noun cwal-m (or kwal-m, qual-m) was derived. Its initial meaning must have been approximately “a mass of fluid or vaporous substance rising (forcefully) to the surface.” Later the noun acquired negative and figurative connotations, such as “thick, suffocating smoke; nausea; torment; daze, stupefaction.” A parallel formation had no suffix (qual). The root dwell- yielded a similar-sounding noun: dwalm (twalm). The meanings of qualm and dwalm sometimes overlapped, but those were distinct (unrelated) words. English borrowed qualm from Low German. The same seems to be true of High German Qualm and of the related Scandinavian nouns, which I have not discussed here, for their history would not have added anything to what we already know.
If the above looks like dry stuff, it has the advantage of offering a solution rather than a vague reference to complexity and ignorance. To make amends, here is a supplement. At one time, the Modern English verb quail “to lose heart, falter, cower” was traced to Old Engl. cwelan “die” and cwellan “kill.” Hensleigh Wedgwood disagreed. He identified quail “falter” with quail “to curdle” and traced it to Latin coagulare “coagulate.” Skeat knew his opinion but believed that the two verbs were homonyms. (The bird name quail is distinct, though it too was once drawn into the picture.)
It is amusing to quote A. L. Mayhew, a good language historian and bellicose critic. With reference to those who treated cwelan or cwellan as the etymon of quail, he wrote (1906): “It never seems to have occurred to these scholars that such an etymology is quite inadmissible, as the vowel sound of quail cannot be made to correspond with the original vowel of Old English cwelan or cwellan. Wedgwood didn’t care a brass button about phonetic laws, but he had a very keen sense for what is probable in the connection and the etymology of our word quail. He says: ‘To quail, as when we speak of one’s courage failing, is probably a special application of quail in the sense of curdle.’…It is the same word as Fr. cailler, to curdle, coagulate, a sister form of which is Ital. cagliare.” The same argument has been made more than once, and Skeat reluctantly changed his opinion.
This brings my blood-curdling story to an end.