The Collaborative International Dictionary of English v.0.48:
Polacca \Po*lac"ca\, n. [It. polacca, polaccra, polacra; cf. F. polaque, polacre, Sp. polacre,] [Written also polacre.] 1. (Naut.) A vessel with two or three masts, used in the Mediterranean. The masts are usually of one piece, and without tops, caps, or crosstrees. [1913 Webster] 2. (Mus.) See Polonaise. [1913 Webster]