viper

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several venomous Old World snakes of the family Viperidae, having a single pair of long, hollow fangs and a thick, heavy body. Also called adder².
2. n. A pit viper.
3. n. A venomous or supposedly venomous snake.
4. n. A person regarded as malicious or treacherous.

Century Dictionary and Cyclopedia

1. n. A venomous snake of the family Viperidæ: originally and especially applied to the only serpent of this kind occurring in the greater part of Europe, Vipera communis Or Pelias beruts. This is the only poisonous reptile which is found in Great Britain, and there it is neither very common nor very dangerous. There are several genera and many species, of vipers properly so called, all Old World, chiefly of warm countries, all poisonous, and most of them very dangerous if not fatal; they are known indifferently as vipers, asps, or adders. See Viperidæ, and cuts under adder, Cerastes, and daboya.
2. n. Any venomous serpent except a rattlesnake; a viperine; a cobriform and not crotali form serpent, as a cobra, asp, or adder; also, loosely, any serpent that is venomous, or supposed to be so; a dangerous, repulsive, or ugly snake. In the United States the name is commonly but erroneously applied to various spotted snakes, especially to some supposed to be venomous, but in fact innocuous: as, the water-viper, Ancistrodon piscivorus, the water-moccasin, poisonous; the blowing-viper and black viper, Heterodon platyrhinos and H. niger, both harmless, though of formidable and repulsive aspect. See cuts under asp, cobra-de-capello, copperhead, moccasin, andpit-viper.
3. n. In heraldry, a serpent used as a bearing, some writers avoid the word serpent and use viper instead, there being no difference in the representations.
4. n. One who or that which is mischievous or malignant.

Wiktionary

1. n. A poisonous snake in the family Viperidae.

GNU Webster's 1913

1. n. Any one of numerous species of Old World venomous snakes belonging to Vipera, Clotho, Daboia, and other genera of the family Viperidæ.
2. n. A dangerous, treacherous, or malignant person.
3. n. Loosely, any venomous or presumed venomous snake.

WordNet 3.0

1. n. venomous Old World snakes characterized by hollow venom-conducting fangs in the upper jaw