- any of several New World pit vipers of the genera Crotalus and Sistrurus, having a rattle composed of a series of horny, interlocking elements at the end of the tail.
- any of the venomous New World snakes constituting the genera Crotalus and Sistrurus, such as C. horridus (black or timber rattlesnake): family Crotalidae (pit vipers). They have a series of loose horny segments on the tail that are vibrated to produce a buzzing or whirring sound
