topgallant n a sail set on a yard of a topgallant mast n a mast fixed to the head of a topmast on a square-rigged vessel Usage(s) It also included some topgallant art. Bisset had six years in sail, scrambling out on the swaying yards to clew up a topgallant sail, growing calluses on his knees from holystoning the wooden decks with "Bibles" (big . Synonym(s) topgallant sail topgallant mast