fire·​fly | \ ˈfī(-ə)r-ˌflī How to pronounce firefly (audio) \

Definition of firefly

: any of various winged nocturnal beetles (especially family Lampyridae) that produce a bright soft intermittent light by oxidation of luciferin especially for courtship purposes

Illustration of firefly

Illustration of firefly

Examples of firefly in a Sentence

Recent Examples on the Web Passenger jets, typically lined up in the night sky, headed to O’Hare International Airport like orderly fireflies, are mostly gone. Peter Slevin, The New Yorker, "Chicago Plans for a Slow Recovery from the Coronavirus," 22 Apr. 2020 His research into the transmission path of H.I.V. and how the virus interacts with other cells in the body led him to use bioluminescence from both fireflies and shrimp to tag and track S.I.V., a similar virus transmitted in macaques. Jill Langlois, Smithsonian, "How Studying Bioluminescent Creatures Is Transforming Medical Science," 5 Dec. 2019 Some of these displays—like the flashes of a firefly or the dances of some colorful birds—are thought to be competitive, with suitors vying for the attention of a mate. Katherine J. Wu, Smithsonian Magazine, "Dolphin Boy Bands Sing ‘Pop’ Songs in Sync—and the Ladies Want It That Way," 1 Apr. 2020 The second-most serious threat to fireflies is considered to be light pollution. Doyle Rice, USA TODAY, "Fireflies face extinction from habitat loss, artificial light and pesticides, study says," 4 Feb. 2020 Some 25 kinds of African animals, from a massive elephant to tiny fireflies, are represented. Jim Higgins, Milwaukee Journal Sentinel, "Meet the animals in 'The Lion King' and see their real-life counterparts at the Milwaukee County Zoo," 29 Jan. 2020 The synchronized displays of other animals—like fireflies that light up at the same time—are thought to be competitive, showing off which male is the sexiest, rather than cooperative. Elizabeth Pennisi, Science | AAAS, "Dolphin ‘gangs’ protect their females by vocalizing in sync," 31 Mar. 2020 Find out—and use that knowledge to your advantage—with this smart Bluetooth sound machine disguised as a jar full of fireflies. Popular Science, "Comforting sound machines for babies," 11 Mar. 2020 Hundreds — maybe thousands — of tiny fireflies swarmed the mangrove tree, visible only by their telltale bioluminescent spark. Alison Fox, Travel + Leisure, "This Dreamy Island in Indonesia Lights Up With Hundreds of Fireflies at Night," 4 Mar. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'firefly.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of firefly

1655, in the meaning defined above

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Time Traveler for firefly

Time Traveler

The first known use of firefly was in 1655

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Statistics for firefly

Last Updated

8 May 2020

Cite this Entry

“Firefly.” Dictionary, Merriam-Webster, Accessed 3 Jun. 2020.

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More Definitions for firefly


How to pronounce firefly (audio)

English Language Learners Definition of firefly

: a small flying insect that produces a soft light


fire·​fly | \ ˈfīr-ˌflī How to pronounce firefly (audio) \
plural fireflies

Kids Definition of firefly

: a small beetle producing a soft light

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More from Merriam-Webster on firefly

Rhyming Dictionary: Words that rhyme with firefly

Spanish Central: Translation of firefly

Nglish: Translation of firefly for Spanish Speakers

Britannica English: Translation of firefly for Arabic Speakers Encyclopedia article about firefly

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