[vi.per] n [MF vipere, fr. L vipera] (1526) 1 a: a common Eurasian venomous snake (Vipera berus) that attains a length of two feet (0.6 meter), varies in color from red, brown, or gray with dark markings to black, and is usu. not fatal to humans; broadly: any of a family (Viperidae) of venomous snakes that includes Old World snakes (subfamily Viperinae) and the pit vipers b: a venomous or reputedly venomous snake
2: a vicious or treacherous person