firefly

American  

[fahyuhr-flahy] / ˈfaɪərˌflaɪ /

noun

fireflies plural

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

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firefly British  

/ ˈfaɪəˌflaɪ /

noun

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

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Other Word Forms

Noun Inflected Forms

• fireflies
  plural

Etymology

Origin of firefly

First recorded in 1650–60; fire + fly ¹

Explanation

Fireflies are flying beetles that glow in the dark. If you gently catch a firefly between your palms, you can watch its light flicker on and off for a while, and then let it go. Depending on where you live, you may call fireflies "lightning bugs" or "glowworms." There are fewer of these light-emitting insects on the planet than there used to be, but you can still find places where they gather in groups at dusk, glowing and flickering like stars. Contrary to their name, fireflies aren't flies, but instead belong to a family of beetles with an amazing ability to produce a luminous light.

Example Sentences

Firefly Aerospace shares traded as high as $30.64, but closed at $28.37, down 3.5%.

From Barron's • Jul. 1, 2026

Intuitive Machines’ stock is up by more than 5%, while Firefly shares are trading 2% higher in early action.

From MarketWatch • Jul. 1, 2026

Coming into Monday trading, shares of Rocket Lab, Firefly, and AST were down an average of 29%, despite SpaceX’s successful IPO.

From Barron's • Jun. 15, 2026

Shares of Rocket Lab are up 4% in early trading Monday, while shares of Firefly are ahead 7%.

From MarketWatch • Jun. 15, 2026

Of course, there are times when a bit of stiffness is appropriate: “I’ve got my reasons for always using like, ’’saidRufus T. Firefly.

From "Woe Is I" by Patricia T. O'Conner