The Collaborative International Dictionary of English v.0.48:

bullsnake \bull"snake`\, bull snake \bull"
snake`\(b[oo^]l"sn[=a]k`), n.
   any of several large harmless rodent-eating North American
   burrowing snakes of the genus Pituophis. They include the
   gopher snake and pine snake.

   Syn: .
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bull-snake
    n 1: any of several large harmless rodent-eating North American
         burrowing snakes [syn: bull snake, bull-snake]