any of various poisonous American pit vipers (genera Crotalus and Sistrurus), having an interlocking series of horny rings at the end of the tail that produce a rattling or buzzing sound when shaken
See rattlesnake in American Heritage Dictionary 4
noun
Any of various venomous New World snakes of the genera Crotalus and Sistrurus, having at the end of the tail a series of loosely attached, horny segments that can be vibrated to produce a rattling or buzzing sound.