firefly

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various nocturnal beetles of the family Lampyridae, characteristically having luminescent chemicals in the posterior tip of the abdomen that produce a flashing light. Also called lightning bug. See Regional Note at lightning bug.

Century Dictionary and Cyclopedia

1. n. An insect which has the faculty of becoming luminous; a lampyrid or elaterid beetle which emits phosphorescent light from organs in some part of the body. One of the commonest American species is a lampyrid, Photinus pyralis, vulgarly called lightning-bug. Its larva lives in the ground, feeding on earthworms and soft-bodied insects, and transforms to the pupa in an oval earthen cell in June, issuing as a beetle ten days later. In the genus Photuris the larva is luminous. The larger tropical fireflies belong to the elaterid genus Pyrophorus, and are known as cucujids. One of the most brilliant is P. noctilucus of South America and the West Indies, emitting such luminosity from two eye-like fenestræ on the thorax that small print may be read by this light. The insects are sometimes used to afford light for domestic purposes, several of them confined together emitting light enough to enable a person to write. The glow-worm is, however, a lampyrid. The lantern-fly is a homopterous insect of a different order.

Wiktionary

1. n. A nocturnal, bioluminescent beetle of the family Lampyridae.

GNU Webster's 1913

1. n. (Zoöl.) Any luminous winged insect, esp. luminous beetles of the family Lampyridæ.

WordNet 3.0

1. n. nocturnal beetle common in warm regions having luminescent abdominal organs
2. n. tropical American click beetle having bright luminous spots