Wordnet 3.0
NOUN (1)
1. 
 small donkey used as a pack animal; 
The Collaborative International Dictionary of English v.0.48:
Burro \Bur"ro\, n. [Sp., an ass.] (Zool.)
   A donkey. [Southern U.S.]
   [1913 Webster]
WordNet (r) 3.0 (2006):
burro
    n 1: small donkey used as a pack animal