Source : Webster's Revised Unabridged Dictionary (1913)

Wiver \Wiv"er\, Wivern \Wiv"ern\, n. [OE. wivere a serpent, OF.
   wivre, guivre, F. givre, guivre, wiver, from L. vipera;
   probably influenced by OHG. wipera, from the Latin. See
   {Viper}, and cf. {Weever}.]
   1. (Her.) A fabulous two-legged, winged creature, like a
      cockatrice, but having the head of a dragon, and without
      spurs. [Written also {wyvern}.]

            The jargon of heraldry, its griffins, its mold
            warps, its wiverns, and its dragons.  --Sir W.
                                                  Scott.

   2. (Zo["o]l.) The weever.

Source : WordNet®

wivern
     n : a fire-breathing dragon used in medieval heraldry; had the
         head of a dragon and the tail of a snake and a body with
         wings and two legs [syn: {wyvern}]