: any of various mostly New World highly specialized venomous snakes (as the rattlesnake, copperhead, water moccasin, and fer-de-lance) that belong to a subfamily (Crotalinae) of the family Viperidae, that have a small depression on each side of the head between the eye and the nostril, and that have hollow perforated fangs usually folded back in the upper part of the mouth but erected in striking
Any species of viper (subfamily Crotalinae) that has, in addition to two movable fangs, a heat-sensitive pit organ between each eye and nostril which together help it accurately aim its strike at its warm-blooded prey. Pit vipers are found from deserts to rain forests, primarily in the New World. They may be terrestrial, arboreal, or aquatic. Some species lay eggs; others produce live young. See alsobushmaster, copperhead, fer-de-lance, moccasin, rattlesnake.