any of a large family (Vespertilionidae) of long-tailed bats that are widely distributed, esp. in temperate regions, including most of the small, insect-eating species
See vespertilionid in American Heritage Dictionary 4
(vĕsˌpər-tĭlˈē-ə-nĭd)
noun
Any of various widely distributed insect-eating bats of the family Vespertilionidae, characterized by a long tail.