To Quack. v.n. [quacken, Dutch, to cry as a goose.]

1. To cry like a duck. This word is often written quaake to represent the sound better.

   Wild-ducks quack where grasshoppers did sing. King.

2. To chatter boastingly; to brag loudly; to talk ostentatiously.

   Believe mechanick virtuosi
   Can raise them mountains in Potosi,
   Seek out for plants with signatures,
   To quack of universal cures. Hudibras, p. iii.