The Collaborative International Dictionary of English v.0.48:

Hadrosaurus \Had`ro*sau"rus\ (h[a^]d`r[-o]*s[add]"r[u^]s), n.
   [NL., fr. Gr. "adro`s thick + say^ros lizard.] (Paleon.)
   An American herbivorous dinosaur of great size, allied to the
   iguanodon. It is found in the Cretaceous formation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hadrosaurus
    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]