The Collaborative International Dictionary of English v.0.48:

Cruiser \Cruis"er\ (kr?"z?r), n.
   One who, or a vessel that, cruises; Specif.: (Nav.) A
   man-of-war less heavily armed and armored than a battle ship,
   having great speed, and generally of from two thousand to
   twelve thousand tons displacement.
   [1913 Webster + Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

cruiser
    n 1: a car in which policemen cruise the streets; equipped with
         radiotelephonic communications to headquarters [syn:
         cruiser, police cruiser, patrol car, police car,
         prowl car, squad car]
    2: a large fast warship; smaller than a battleship and larger
       than a destroyer
    3: a large motorboat that has a cabin and plumbing and other
       conveniences necessary for living on board [syn: cabin
       cruiser, cruiser, pleasure boat, pleasure craft]