noun
: any of various mostly New World highly specialized venomous snakes (as the rattlesnake, copperhead, water moccasin, fer-de-lance) that have a small depression on each side of the head between the eye and the nostril which is lined with sensory epithelium and innervated by branches of the trigeminal nerve, that have hollow perforated fangs usually folded back in the upper part of the mouth but erected in striking, and that constitute the family Crotalidae