1911 Encyclopædia Britannica/Quack
QUACK, one who pretends to knowledge of which he is ignorant, a charlatan, particularly a medical impostor. The word is a shortened form of “quacksalver” (Du. kwaksalver), in which form it is common in the 17th century, “salver” meaning “healer,” while “quack” (Du. kwakken) is merely an application of the onomatopoeic word applied to the sounds made by a duck, i.e. gabble or gibberish. In English law, to call a medical practitioner a “quack” is actionable per se without proof of special damage (Allen v. Eaton (1630), 1 Roll. Abs. 54). The often-quoted legal definition of a “quack” is “a boastful pretender to medical skill,” but a “quack” may have great skill, and it is the claim to cure by remedies which he knows have no efficacy which makes him a “quack” (see Dakhyl v. Labouchere, The Times, 29th of July 1904, and 5th and 9th of November 1907).