Definition of vampire bat
:any of several bats (Desmodus rotundus, Diaemus youngi, and Diphylla ecaudata of the subfamily Desmodontinae of the family Phyllostomidae) of Mexico and Central and South America that feed on the blood of birds and mammals and especially domestic animals and that are sometimes vectors of disease and especially of rabies;
also
:any of several other bats (as of the families Megadermatidae and Phyllostomidae) that do not feed on blood but are sometimes reputed to do so
