The Collaborative International Dictionary of English v.0.48:

Megalosaur \Meg"a*lo*saur`\, Megalosaurus \Meg`a*lo*sau"rus\, n.
   [NL. megalosaurus, fr. Gr. me`gas, mega`lh, great + say^ros
   lizard: cf. F. m['e]galosaure.] (Paleon.)
   A gigantic carnivorous dinosaur, whose fossil remains have
   been found in England and elsewhere.
   [1913 Webster]

WordNet (r) 3.0 (2006):

megalosaurus
    n 1: gigantic carnivorous bipedal dinosaur of the Jurassic or
         early Cretaceous in Europe [syn: megalosaur,
         megalosaurus]