canard n.

"medical charlatan, impudent and fraudulent pretender to medical skill," 1630s, short for quacksalver (1570s), from obsolete Dutch quacksalver (modern kwakzalver), literally "hawker of salve," from Middle Dutch quacken "to brag, boast," literally "to croak" (see quack (v.)) + salf "salve," salven "to rub with ointment" (see salve (n.)). As an adjective from 1650s.

The oldest attested form of this quack in English is as a verb, "to play the quack" (1620s). The Dutch word also is the source of German Quacksalber, Danish kvaksalver, Swedish kvacksalvare.

A quack is, by derivation, one who talks much without wisdom, and, specifically, talks of his own power to heal ; hence, any ignorant pretender to medical knowledge or skill. Empiric is a more elevated term for one who goes by mere experience in the trial of remedies, and is without knowledge of the medical sciences or of the clinical observations and opinions of others; hence, an incompetent, self-confident practitioner. A mountebank is generally a quack, but may be a pretender in any line. Charlatan (literally 'chatterer') is primarily applied, not to a person belonging to any particular profession or occupation, but to a pretentious cheat of any sort. [Century Dictionary, 1897]

 Also "one who pretends to knowledge of any kind" (1630s).

also can-can, "A kind of dance performed in low resorts by men and women, who indulge in extravagant postures and lascivious gestures" [Century Dictionary, 1895], 1848, from French, a slang or cant term possibly from can, a French children's word for "duck" (see canard), via some notion of "waddling" too obscure or obscene to attempt to disentangle here. Or perhaps from French cancan (16c.) "noise, disturbance," echoic of quacking.