Firefly \Fire"fly`\, n.; pl. {Fireflies}. (Zo["o]l.) Any luminous winged insect, esp. luminous beetles of the family {Lampyrid[ae]}. Note: The common American species belong to the genera {Photinus} and {Photuris}, in which both sexes are winged. The name is also applied to luminous species of {Elaterid[ae]}. See {Fire beetle}.