QUACK, v.i.

1. To cry like a duck or goose.

2. To boast; to bounce; to talk noisily and ostentatiously; as, pretenders to medical skill quack of their cures.

QUACK, n. [from the verb.]

1. A boaster; one who pretends to skill or knowledge which he does not possess.

2. A boastful pretender to medical skill which he does not possess; an empiric; an ignorant practitioner.