viper

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various venomous snakes of the family Viperidae, having a thick heavy body and a single pair of long hollow fangs, especially the Eurasian and African species of the subfamily Viperinae, which lack the sensory pits of the pit vipers.
• noun Any of several harmless snakes sometimes believed to be venomous.
• noun A person regarded as malicious or treacherous.

from The Century Dictionary.

• noun 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.
• noun 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.
• noun 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.
• noun One who or that which is mischievous or malignant.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) Any one of numerous species of Old World venomous snakes belonging to Vipera, Clotho, Daboia, and other genera of the family Viperidæ.
• noun A dangerous, treacherous, or malignant person.
• noun Loosely, any venomous or presumed venomous snake.
• noun (Zoöl.) See Cerastes.
• noun (Zoöl.) the copperhead.
• noun (Zoöl.) a small, slender, phosphorescent deep-sea fish (Chauliodus Sloanii). It has long ventral and dorsal fins, a large mouth, and very long, sharp teeth.
• noun (Bot.) a rough-leaved biennial herb (Echium vulgare) having showy purplish blue flowers. It is sometimes cultivated, but has become a pestilent weed in fields from New York to Virginia. Also called blue weed.
• noun (Bot.) a perennial composite herb (Scorzonera Hispanica) with narrow, entire leaves, and solitary heads of yellow flowers. The long, white, carrot-shaped roots are used for food in Spain and some other countries. Called also viper grass.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A poisonous snake in the family Viperidae.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun venomous Old World snakes characterized by hollow venom-conducting fangs in the upper jaw