"flying mammal" (order Chiroptera), 1570s, a dialect alteration of M.E. bakke, which is probably related to O.Swed. natbakka, O.Dan. nathbakkæ "night bat," and O.N. leðrblaka "leather flapper," so original sense is likely "flapper." The shift from -k- to -t- may have come through confusion
of bakke with L. blatta "moth, nocturnal insect." O.E. word for the animal was hreremus, from hreran "to shake." As a contemptuous term for an old woman, perhaps a suggestion of witchcraft (cf. fly-by-night
), or from bat as "prostitute who plies her trade by night" [Farmer, who calls it "old slang" and finds Fr. equivalent "night swallow" (hirondelle de nuit) "more poetic"].
"to move the eyelids," 1847, Amer.Eng., from earlier sense of "flutter as a hawk" (1610s), a variant of bate
(2) on the notion of fluttering wings.