Source : Webster's Revised Unabridged Dictionary (1913)

Rattlesnake \Rat"tle*snake`\, n. (Zo["o]l.)
   Any one of several species of venomous American snakes
   belonging to the genera {Crotalus} and {Caudisona}, or
   {Sistrurus}. They have a series of horny interlocking joints
   at the end of the tail which make a sharp ratting sound when
   shaken. The common rattlesnake of the Northern United States
   ({Crotalus horridus}), and the diamond rattlesnake of the
   south ({C. adamanteus}), are the best known. See Illust. of
   {Fang}.

Source : WordNet®

rattlesnake
     n : pit viper with horny segments at the end of the tail that
         rattle when shaken [syn: {rattler}]