Illustration of firefly
firefly
noun
fire·fly
ˈfī(-ə)r-ˌflī 
: any of various winged nocturnal beetles (especially family Lampyridae) that produce a bright soft intermittent light by oxidation of luciferin especially for courtship purposes
Examples of firefly in a Sentence
Recent Examples on the Web
Compared to the more common white or yellow flashes from other species, blue ghost fireflies fly low to the forest floor with a steady light.
—
Meghan Overdeep, Southern Living, 13 Apr. 2025
The Blue Ghost spacecraft, named for a species of firefly, took eclipse chasing to new heights.
—Ars Technica, 18 Mar. 2025
In April and May, when temperatures are still cool enough to enjoy a soak, the forest surrounding the hotel fills with fireflies at dusk, making a delightful evening show.
—Clarissa Wei, AFAR Media, 3 Feb. 2025
Karl Leitz Japan’s Firefly Squid Is Embraced by Chefs Stateside
Editors’ Picks
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Each spring, hotaru ika, or firefly squid, ascend to the surface of western Japan’s Toyama Bay to spawn, setting the water aglow with pinpricks of electric blue light.
—New York Times, 19 Feb. 2025
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Meghan Overdeep, Southern Living, 13 Apr. 2025
The Blue Ghost spacecraft, named for a species of firefly, took eclipse chasing to new heights.
—Ars Technica, 18 Mar. 2025
In April and May, when temperatures are still cool enough to enjoy a soak, the forest surrounding the hotel fills with fireflies at dusk, making a delightful evening show.
—Clarissa Wei, AFAR Media, 3 Feb. 2025
Karl Leitz Japan’s Firefly Squid Is Embraced by Chefs Stateside
Editors’ Picks
Image
Each spring, hotaru ika, or firefly squid, ascend to the surface of western Japan’s Toyama Bay to spawn, setting the water aglow with pinpricks of electric blue light.
—New York Times, 19 Feb. 2025
See All Example Sentences for firefly
Cite this Entry
“Firefly.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/firefly. Accessed 24 Apr. 2025.
Copy CitationKids Definition
firefly
noun
fire·fly
ˈfī(ə)r-ˌflī
: any of numerous night-flying beetles that produce a bright soft flashing light for courtship purposes
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