Source : Webster's Revised Unabridged Dictionary (1913)

Brontosaurus \Bron`to*sau"rus\, n. [NL., fr. Gr. ? thunder + ?
   lizard.] (Paleon.)
   A genus of American jurassic dinosaurs. A length of sixty
   feet is believed to have been attained by these reptiles.

Source : WordNet®

brontosaurus
     n : huge quadrupedal herbivorous dinosaur common in North
         America in the late Jurassic [syn: {apatosaur}, {apatosaurus},
          {brontosaur}, {thunder lizard}, {Apatosaurus excelsus}]