The Collaborative International Dictionary of English v.0.48:

Gibbon \Gib"bon\, n. [Cf. F. gibbon.] (Zool.)
   Any arboreal ape of the genus Hylobates, of which many
   species and varieties inhabit the East Indies and Southern
   Asia. They are tailless and without cheek pouches, and have
   very long arms, adapted for climbing.

   Note: The white-handed gibbon (Hylobates lar), the crowned
         (H. pilatus), the wou-wou or singing gibbon (H.
         agilis), the siamang, and the hoolock. are the most
         common species.
         [1913 Webster]