quack

quack · noun, verb, interjection¹

1. Proto-Germanic · derived from*kwakaną
2. Proto-West Germanic · derived from*kwakōn
3. Old Dutch · derived from*kwaken“to croak, quack”
4. Middle Dutch · derived fromquacken“to croak, quack”
5. Middle English · inherited from*quacken
6. English todayquack

From Middle English *quacken, queken (“to croak like a frog; make a noise like a duck, goose, or quail”), from quack, qwacke, quek, queke (“quack”, interjection and noun), also kek, keke, whec-, partly of imitative origin and partly from Middle Dutch quacken (“to croak, quack”), from Old Dutch *kwaken (“to croak, quack”), from Proto-West Germanic *kwakōn, from Proto-Germanic *kwakaną, *kwakōną (“to croak”), of imitative origin. Cognate with Saterland Frisian kwoakje, kwaakje (“to quack”), Middle Low German quaken (“to quack, croak”), German quaken (“to quack, croak”), Danish kvække (“to croak”), Swedish kväka (“to croak, quackle”), Norwegian kvekke (“to croak”), Icelandic kvaka (“to twitter, chirp, quack”).

quack · noun, verb, adjective²

1. Middle Dutchquacsalven
2. Dutchquacksalver
3. Englishquacksalverclip.
4. English todayquack

Clipping of quacksalver (see there for more), of Dutch origin; ultimately related to Etymology 1 above.

First known use, by meaning

• from c. 1630 A fraudulent healer, especially a bombastic peddler in worthless treatments, a doctor who makes false diagnoses for monetary benefit, or an untrained or poorly trained doctor who uses fraudulent credentials to attract patients