The Collaborative International Dictionary of English v.0.48:

Wolfhound \Wolf"hound`\, n. (Zool.)
   Originally, a large hound used in hunting wolves; now, any
   one of certain breeds of large dogs, some of which are nearly
   identical with the great Danes.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

wolfhound
    n 1: the largest breed of dogs; formerly used to hunt wolves