The Collaborative International Dictionary of English v.0.48:

Boa constrictor \Bo"a con*strict"or\ [NL. See Boa, and
   Constrictor.] (Zool.)
   A large and powerful serpent of tropical America, sometimes
   twenty or thirty feet long. See Illustration in Appendix.
   [1913 Webster]

   Note: It has a succession of spots, alternately black and
         yellow, extending along the back. It kills its prey by
         constriction. The name is also loosely applied to other
         large serpents which crush their prey, particularly to
         those of the genus Python, found in Asia and Africa.
         [1913 Webster]

WordNet (r) 3.0 (2006):

boa constrictor
    n 1: very large boa of tropical America and West Indies [syn:
         boa constrictor, Constrictor constrictor]