The Collaborative International Dictionary of English v.0.48:

Tamarin \Tam"a*rin\, n. [From the native name in Cayenne.]
   (Zool.)
   Any one of several species of small squirrel-like South
   American monkeys of the genus Midas, especially Midas
   ursulus.
   [1913 Webster]
   [1913 Webster]

WordNet (r) 3.0 (2006):

tamarin
    n 1: small South American marmoset with silky fur and long
         nonprehensile tail [syn: tamarin, lion monkey, lion
         marmoset, leoncita]