Source : Webster's Revised Unabridged Dictionary (1913)

Werewolf \Were"wolf`\, n.; pl. {Werewolves}. [AS. werwulf; wer a
   man + wulf a wolf; cf. G. w["a]rwolf, w["a]hrwolf, wehrwolf,
   a werewolf, MHG. werwolf. [root]285. See {Were} a man, and
   {Wolf}, and cf. {Virile}, {World}.]
   A person transformed into a wolf in form and appetite, either
   temporarily or permanently, whether by supernatural
   influences, by witchcraft, or voluntarily; a lycanthrope.
   Belief in werewolves, formerly general, is not now extinct.

         The werwolf went about his prey.         --William of
                                                  Palerne.

         The brutes that wear our form and face, The werewolves
         of the human race.                       --Longfellow.

Source : WordNet®

werewolf
     n : a monster able to change appearance from human to wolf [syn:
          {wolfman}, {lycanthrope}]
     [also: {werewolves} (pl)]