Crotalus

from WordNet (r) 3.0 (2006)

Crotalus
    n 1: large rattlesnakes; seldom bite unless startled or pursuing
         prey [syn: {Crotalus}, {genus Crotalus}]

from The Collaborative International Dictionary of English v.0.48

Crotalus \Crot"a*lus\ (-l?s), n. [NL., fr. Gr. ???? rattle.]
   (Zool.)
   A genus of poisonous serpents, including the rattlesnakes.
   [1913 Webster]