coypu

from WordNet (r) 3.0 (2006)

coypu
    n 1: aquatic South American rodent resembling a small beaver;
         bred for its fur [syn: {coypu}, {nutria}, {Myocastor
         coypus}]

from The Collaborative International Dictionary of English v.0.48

Coypu \Coy"pu\ (koi"p??), n. [Native name.] (Zool.)
   A South American rodent ({Myopotamus coypus}), allied to the
   beaver. It produces a valuable fur called {nutria}. [Written
   also {coypou}.]
   [1913 Webster]