The Collaborative International Dictionary of English v.0.48:

ceratosaur \ceratosaur\ n. (Paleon.)
   the ceratosaurus.

   Syn: ceratosaurus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

ceratosaur
    n 1: primitive medium-sized theropod; swift-running bipedal
         carnivorous dinosaur having grasping hands with sharp claws
         and a short horn between the nostrils; Jurassic in North
         America [syn: ceratosaur, ceratosaurus]