mizzenmast

n. (Naut.) the third mast from the bow in a vessel having three or more masts; the after and shorter mast of a yawl, ketch, or dandy. The definition varies slightly with the dictionary; in some dictionaries it is the last mast of a three-masted vessel; in others, it is the mast after the mainmast of a vessel of three or more masts. PJC. [ 1913 Webster + WordNet 1.5 ]