- any of numerous venomous snakes of the family Crotalidae, of the New World, Asia, and the Malay Archipelago, as the rattlesnake, water moccasin, and copperhead, having a heat-sensitive pit on each side of the head between the eye and nostril.
- any venomous snake of the New World family Crotalidae, having a heat-sensitive organ in a pit on each side of the head: includes the rattlesnakes
- Any of various very venomous snakes of the family Crotalidae. Pit vipers are characterized by a triangular head with a small sensory pit below each eye. The pits detect infrared radiation and help the snake locate prey. Some scientists classify the pit vipers as a subfamily Crotalinae within the Viperidae, the family of vipers, rather than as a separate family. Copperheads, rattlesnakes, and fer-de-lances are pit vipers.