The Collaborative International Dictionary of English v.0.48:

Unau \U*nau"\ ([-u]*n[add]"), n. [Brazilian.] (Zool.)
   The two-toed sloth (Cholopus didactylus), native of South
   America. It is about two feet long. Its color is a uniform
   grayish brown, sometimes with a reddish tint.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unau
    n 1: a sloth of Central America that has two long claws on each
         forefoot and three long claws on each hindfoot [syn: two-
         toed sloth, unau, unai, Choloepus hoffmanni]
    2: relatively small fast-moving sloth with two long claws on
       each front foot [syn: two-toed sloth, unau, unai,
       Choloepus didactylus]