Quack (?), v. i. [imp. & p. p.Qvacked (?); p. pr. & vb. n.Quacking.] [Of imitative origin; cf. D. kwaken, G. quacken, quaken, Icel. kvaka to twitter.]
1. To utter a sound like the cry of a duck.
2. To make vain and loud pretensions; to boast. “ To quack of universal cures.” Hudibras.
3. To act the part of a quack, or pretender.