- quack (v.)
- "to make a duck sound," 1610s, quelke, of echoic origin (cf. Middle Dutch quacken, Old Church Slavonic kvakati, Latin coaxare "to croak," Greek koax "the croaking of frogs," Hittite akuwakuwash "frog"). Middle English on the quakke (14c.) meant "hoarse, croaking." Related: Quacked; quacking.
- quack (n.)
- "medical charlatan," 1630s, short for quacksalver (1570s), from Dutch kwaksalver, literally "hawker of salve," from Middle Dutch quacken "to brag, boast," literally "to croak" (see quack (v.)) + zalf "salve" (see salve (v.)). Cf. German Quacksalber, Danish kvaksalver, Swedish kvacksalvare.