The Collaborative International Dictionary of English v.0.48:

Hornbill \Horn"bill`\, n. (Zool.)
   Any bird of the family Bucerotid[ae], of which about sixty
   species are known, belonging to numerous genera. They inhabit
   the tropical parts of Asia, Africa, and the East Indies, and
   are remarkable for having a more or less horn-like
   protuberance, which is usually large and hollow and is
   situated on the upper side of the beak. The size of the
   hornbill varies from that of a pigeon to that of a raven, or
   even larger. They feed chiefly upon fruit, but some species
   eat dead animals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hornbill
    n 1: bird of tropical Africa and Asia having a very large bill
         surmounted by a bony protuberance; related to kingfishers