The Collaborative International Dictionary of English v.0.48:

ceratopsian \ceratopsian\ n.
   any of several four-footed herbivorous horned dinosaurs with
   enormous beaked skulls, of the late Cretaceous in North
   America and Mongolia.

   Syn: horned dinosaur.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

ceratopsian
    n 1: any of several four-footed herbivorous dinosaurs with
         enormous beaked skulls; of the late Cretaceous in North
         America and Mongolia [syn: ceratopsian, horned
         dinosaur]