Pronunciation: (vī'pur),[key] —n. 1. any of several venomous Old World snakes of the genus Vipera, esp. V. berus, a small snake common in northern Eurasia.
2. any related snakes belonging to the family Viperidae, characterized by erectile, venom-conducting fangs.
3. See pit viper. 4. any of various venomous or supposedly venomous snakes.
5. a malignant or spiteful person.
6. a false or treacherous person.
7. (cap.) Mil.a 9-pound (4 kg), shoulder-launched, unguided U.S. Army antitank rocket with an effective range of 273 yds. (250 m).
8. to nourish a viper in one's bosom, to befriend a person who proves to be treacherous.