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From The Collaborative International Dictionary of English v.0.48:
Firefly \Fire"fly`\, n.; pl. Fireflies. (Zool.) Any luminous winged insect, esp. luminous beetles of the family Lampyrid[ae]. [1913 Webster] Note: The common American species belong to the genera Photinus (especially Photinus pyralis) and Photuris, in which both sexes are winged. The name is also applied to luminous species of Elaterid[ae]. See Fire beetle. [1913 Webster +PJC]