The Collaborative International Dictionary of English v.0.48:

hadrosaur \hadrosaur\ n.
   Any member of the genus Hadrosaurus or family
   Hadrosauridae, an extinct family of heavy bipedal partly
   aquatic dinosaurs with duck-billed skull and webbed feet; of
   the Upper Cretaceous in North America.

   Syn: hadrosaurus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

hadrosaur
    n 1: any of numerous large bipedal ornithischian dinosaurs
         having a horny duck-like bill and webbed feet; may have
         been partly aquatic [syn: hadrosaur, hadrosaurus,
         duck-billed dinosaur]