The Collaborative International Dictionary of English v.0.48:

viper \vi"per\ (v[imac]"p[~e]r), n. [F. vip[`e]re, L. vipera,
   probably contr. fr. vivipera; vivus alive + parere to bring
   forth, because it was believed to be the only serpent that
   brings forth living young. Cf. Quick, a., Parent,
   Viviparous, Wivern, Weever.]
   [1913 Webster]
   1. (Zool.) Any one of numerous species of Old World venomous
      snakes belonging to Vipera, Clotho, Daboia, and
      other genera of the family Viperidae.
      [1913 Webster]

            There came a viper out of the heat, and fastened on
            his hand.                             --Acts xxviii.
                                                  3.
      [1913 Webster]

   Note: Among the best-known species are the European adder
         (Pelias berus), the European asp (Vipera aspis),
         the African horned viper (Vipera cerastes), and the
         Indian viper (Daboia Russellii).
         [1913 Webster]

   2. A dangerous, treacherous, or malignant person.
      [1913 Webster]

            Who committed
            To such a viper his most sacred trust
            Of secrecy.                           --Milton.
      [1913 Webster]

   3. Loosely, any venomous or presumed venomous snake.
      [PJC]

   Horned viper. (Zool.) See Cerastes.

   Red viper (Zool.), the copperhead.

   Viper fish (Zool.), a small, slender, phosphorescent
      deep-sea fish (Chauliodus Sloanii). It has long ventral
      and dorsal fins, a large mouth, and very long, sharp
      teeth.

   Viper's bugloss (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.

   Viper's grass (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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

blueweed \blue"weed\ n.
   a coarse prickly European weed (Echium vulgare) with spikes
   of blue flowers; naturalized in the U. S.

   Syn: blue devil, blue thistle, viper's bugloss.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Echium vulgare
    n 1: a coarse prickly European weed with spikes of blue flowers;
         naturalized in United States [syn: blueweed, blue
         devil, blue thistle, viper's bugloss, Echium
         vulgare]