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. kwaksafaer) , 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), i 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. Labotichere, The Times, 29th of July 1904, and 5th and 9th of November 1907).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)