The Collaborative International Dictionary of English v.0.48:

Xebec \Xe"bec\ (z[=e]"b[e^]k), n. [Sp. jabegue, formerly spelt
   xabeque, or Pg. xabeco; both from Turk. sumbeki a kind of
   Asiatic ship; cf. Per. sumbuk, Ar. sumb[=u]k a small ship.]
   (Naut.)
   A small three-masted vessel, with projecting bow and stern
   and convex decks, used in the Mediterranean for transporting
   merchandise, etc. It carries large square sails, or lateen
   sails, or both. Xebecs were formerly armed and used by
   corsairs.
   [1913 Webster]