Source : Webster's Revised Unabridged Dictionary (1913)

Boatswain \Boat"swain\, n. [Boat + swain.]
   1. (Naut.) An officer who has charge of the boats, sails,
      rigging, colors, anchors, cables, cordage, etc., of a
      ship, and who also summons the crew, and performs other
      duties.

   2. (Zo["o]l.)
      (a) The jager gull.
      (b) The tropic bird.

   {Boatswain's mate}, an assistant of the boatswain. --Totten.

Source : WordNet®

boatswain
     n : a petty officer on a merchant ship who controls the work of
         other seamen [syn: {bos'n}, {bo's'n}, {bosun}, {bo'sun}]