firefly

[fahyuh r-flahy] /ˈfaɪərˌflaɪ/
noun, plural fireflies.
1.
any nocturnal beetle of the family Lampyridae, characterized by a soft body with a light-producing organ at the rear of the abdomen.
Also called glowfly, lightning bug.
Compare glowworm.
Origin
1650-60; fire + fly2
British Dictionary definitions for firefly

firefly

/ˈfaɪəˌflaɪ/
noun (pl) -flies
1.
any nocturnal beetle of the family Lampyridae, common in warm and tropical regions, having luminescent abdominal organs See also glow-worm
2.
any tropical American click beetle of the genus Pyrophorus, esp P. noctiluca, that have luminescent thoracic organs
Word Origin and History for firefly
n.

1650s, from fire (n.) + fly (n.).