The Collaborative International Dictionary of English v.0.48:

Vampire \Vam"pire\, n. [F. vampire (cf. It. vampiro, G. & D.
   vampir), fr. Servian vampir.] [Written also vampyre.]
   1. A blood-sucking ghost; a soul of a dead person
      superstitiously believed to come from the grave and wander
      about by night sucking the blood of persons asleep, thus
      causing their death. This superstition was once prevalent
      in parts of Eastern Europe, and was especially current in
      Hungary about the year 1730. The vampire was often said to
      have the ability to transform itself into the form of a
      bat, as presented in the novel depicting the legend of
      Dracula published by Bram Stoker in 1897, which has
      inspired several movies.
      [1913 Webster + PJC]

            The persons who turn vampires are generally wizards,
            witches, suicides, and persons who have come to a
            violent end, or have been cursed by their parents or
            by the church,                        --Encyc. Brit.
      [1913 Webster]

   2. Fig.: One who lives by preying on others; an extortioner;
      a bloodsucker.
      [1913 Webster]

   3. (Zool.) Either one of two or more species of South
      American blood-sucking bats belonging to the genera
      Desmodus and Diphylla; also called vampire bat.
      These bats are destitute of molar teeth, but have strong,
      sharp cutting incisors with which they make punctured
      wounds from which they suck the blood of horses, cattle,
      and other animals, as well as man, chiefly during sleep.
      They have a caecal appendage to the stomach, in which the
      blood with which they gorge themselves is stored.
      [1913 Webster]

   4. (Zool.) Any one of several species of harmless tropical
      American bats of the genus Vampyrus, especially
      Vampyrus spectrum. These bats feed upon insects and
      fruit, but were formerly erroneously supposed to suck the
      blood of man and animals. Called also false vampire.
      [1913 Webster]

   Vampire bat (Zool.), a vampire, 3.
      [1913 Webster]
      [1913 Webster]

WordNet (r) 3.0 (2006):

vampire bat
    n 1: any of various tropical American bats of the family
         Desmodontidae that bite mammals and birds to feed on their
         blood [syn: vampire bat, true vampire bat]