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.