viper

Concise Oxford English Dictionary © 2008 Oxford University Press:
viper /ˈvʌɪpə/

▶noun

• 1 a venomous snake with large hinged fangs, typically with dark patterns on a lighter background. [Vipera berus (the adder) and other species, family Viperidae.]

• 2 a spiteful or treacherous person.

– derivatives
viperine /-rʌɪn/ adjective,
viperish adjective,
viperous adjective.

– origin C16: from Fr. vipère or L. vipera, from vivus ‘alive’ + parere ‘bring forth’ (with ref. to the former belief that vipers bore live young).