The Collaborative International Dictionary of English v.0.48:

Gila monster \Gi"la mon"ster\ (Zool.)
   A large tuberculated lizard (Heloderma suspectum) native of
   the dry plains of Arizona, New Mexico, etc. It is the only
   lizard known to have venomous teeth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Heloderma suspectum
    n 1: large orange and black lizard of southwestern United
         States; not dangerous unless molested [syn: Gila monster,
         Heloderma suspectum]