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]

The Collaborative International Dictionary of English v.0.48:

Polacre \Po*la"cre\, n.
   Same as Polacca, 1.
   [1913 Webster]