- any of several venomous Old World snakes of the genus Vipera, especially V. berus, a small snake common in northern Eurasia.
- any related snakes belonging to the family Viperidae, characterized by erectile, venom-conducting fangs.
- pit viper.
- any of various venomous or supposedly venomous snakes.
- a malignant or spiteful person.
- a false or treacherous person.
- a 9-pound (4-kilogram), shoulder-launched, unguided U.S. Army antitank rocket with an effective range of 273 yards (250 meters).
- to befriend a person who proves to be treacherous.
- any venomous Old World snake of the family Viperidae, esp any of the genus Vipera (the adder and related forms), having hollow fangs in the upper jaw that are used to inject venom
- any of various other snakes, such as the horned viper
- See pit viper
- a malicious or treacherous person
