The Collaborative International Dictionary of English v.0.48:

Anaconda \An`a*con"da\, n. [Of Ceylonese origin?] (Zool.)
   A large South American snake of the Boa family (Eunectes
   murinus), which lives near rivers, and preys on birds and
   small mammals. The name is also applied to a similar large
   serpent (Python tigris) of Ceylon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

anaconda
    n 1: large arboreal boa of tropical South America [syn:
         anaconda, Eunectes murinus]