firefly

noun, plural fire·flies.

1. any nocturnal beetle of the family Lampyridae, characterized by a soft body with a light-producing organ at the rear of the abdomen.

noun plural -flies

1. any nocturnal beetle of the family Lampyridae, common in warm and tropical regions, having luminescent abdominal organsSee also glow-worm
2. any tropical American click beetle of the genus Pyrophorus, esp P. noctiluca, that have luminescent thoracic organs