The Collaborative International Dictionary of English v.0.48:

bonobo \bo*no"bo\ (b[-o]*n[=o]"b[=o]), n.
   An anthropoid ape (Pan paniscus), resembling but smaller
   than the common chimpanzee (Pan troglodytes); -- called
   also pygmy chimpanzee. It is found in the forests of Zaire.
   Its genome is the closest known to humans, differing by less
   than 2% in nucleotide sequence.

   Syn: pygmy chimpanzee, pygmy chimp.
        [PJC]

WordNet (r) 3.0 (2006):

bonobo
    n 1: small chimpanzee of swamp forests in Zaire; a threatened
         species [syn: pygmy chimpanzee, bonobo, Pan paniscus]