Definition of: viper

(vī′pər) noun
1. Any of a family (Viperidae) of venomous Old World snakes, especially the common European viper or adder (Vipera berus), about two feet long and variously colored; also, the African puff adder, and the horned viper.
2. One of a family (Crotalidae) of typically American poisonous snakes, the pit vipers, including the rattlesnake, copper-head, and fer–de–lance, which are characterized by a small depression between the nostril and the eye.
3. Any poisonous or allegedly poisonous snake.
4. A venomous, malicious, treacherous, or spiteful person.
5. U.S. Slang A marihuana smoker. [<OF vipere, vipre <L vipera, contraction of vivipara <vivus living + parere bring forth]
—vi·per·ine (vi′·pər·in, -pə·rīn) adjective
—vi′per·ish adjective