The Collaborative International Dictionary of English v.0.48:

Torpedo-boat destroyer \Tor*pe"do-boat` de*stroy"er\
   A larger, swifter, and more powerful armed type of torpedo
   boat, originally intended principally for the destruction of
   torpedo boats, but later used also as a more formidable
   torpedo boat.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

torpedo-boat destroyer
    n 1: small destroyer that was the forerunner of modern
         destroyers; designed to destroy torpedo boats