pit viper [AS, pytt + L, vipera, snake] , any one of a family of venomous snakes found in the Western Hemisphere and Asia, characterized by a heat-sensitive pit between the eye and nostril on each side of the head and hollow perforated fangs that are usually folded back in the roof of the mouth. With the exception of coral snakes, all indigenous poisonous snakes in the United States are pit vipers. See also copperhead, cottonmouth, rattlesnake.
