The Collaborative International Dictionary of English v.0.48:

Guan \Guan\ (gw[aum]n), n. ((Zool.)
   Any one of many species of large gallinaceous birds of
   Central and South America, belonging to Penelope, Pipile,
   Ortalis, and allied genera. Several of the species are
   often domesticated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

guan
    n 1: any of several large turkey-like game birds of the family
         Cracidae; native to jungles of tropical America; resembling
         the curassows and valued as food