The Collaborative International Dictionary of English v.0.48:

Destroyer \De*stroy"er\, n. [Cf. OF. destruior.]
   1. One who destroys, ruins, kills, or desolates.
      [1913 Webster]

   2. (Nav.) a small fast warship used primarily as an escort to
      larger vessels and typically armed with a combination of
      5-inch guns, torpedos, depth charges, and missiles;
      formerly identical to the Torpedo-boat destroyer.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

destroyer
    n 1: a small fast lightly armored but heavily armed warship
         [syn: destroyer, guided missile destroyer]
    2: a person who destroys or ruins or lays waste to; "a destroyer
       of the environment"; "jealousy was his undoer"; "uprooters of
       gravestones" [syn: destroyer, ruiner, undoer, waster,
       uprooter]