fire·​fly | \ˈfī(-ə)r-ˌflī \

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

Traveling during the summer to conduct field work, Shimomura studied bioluminescent fireworms in Bermuda, cave worms and limpets in New Zealand, and a plethora of glowing bacteria, twinkling fireflies and neon-colored squid and krill. Harrison Smith, The Seattle Times, "Osamu Shimomura, atomic blast survivor and Nobel-winning chemist, dies at 90," 23 Oct. 2018 High grasses and shrubbery are a key part of a firefly’s ideal habitat. Rebecca Straus, Good Housekeeping, "5 Ways to Attract Fireflies to Your Yard," 19 July 2018 But if the brightest fireflies instead converge at the jar’s bottom and top, its glow will peak at those points instead. Shannon Hall, Scientific American, "The Sun Is Spitting Out Strange Patterns of Gamma Rays—and No One Knows Why," 28 Mar. 2018 There were also fireflies everywhere on the big lawn, which the children chased around all evening once the weather cleared. Fortune, "'Glamping' Has Officially Come to New York City," 12 July 2018 Nothing more than a gentle breeze stirs the air, as fireflies dance and occasional growls emanate from the storm cloud. Matthew Cappucci, Washington Post, "Bolts from the blue: Here’s how lightning can strike when a storm is tens of miles away," 27 June 2018 Both males and females flicker, and every species of firefly has evolved a unique code to help potential mates cut through the noise. Katherine J. Wu, Smithsonian, "Why Bioluminescence Evolved to Be Red Light, and Blue," 26 June 2018 Plant Native Pine Trees One of the biggest threats to fireflies is habitat loss. Rebecca Straus, Good Housekeeping, "6 Ways To Attract Fireflies To Your Yard," 9 June 2016 This is akin to how a firefly or a glow-stick generates its light. Kevin Davenport, idahostatesman, "O say can you see? The science behind the booms and blooms of Independence Day fireworks," 3 July 2018

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.

See More

First Known Use of firefly

1655, in the meaning defined above

Keep scrolling for more

Learn More about firefly

Statistics for firefly

Last Updated

21 Nov 2018

Look-up Popularity

Time Traveler for firefly

The first known use of firefly was in 1655

See more words from the same year

Keep scrolling for more

More Definitions for firefly



English Language Learners Definition of firefly

: a small flying insect that produces a soft light


fire·​fly | \ˈfīr-ˌflī \
plural fireflies

Kids Definition of firefly

: a small beetle producing a soft light

Keep scrolling for more

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

Comments on firefly

What made you want to look up firefly? Please tell us where you read or heard it (including the quote, if possible).


a nest or breeding place

Get Word of the Day daily email!

Test Your Vocabulary

Late Autumn 2018 Words of the Day Quiz

  • frosted-autumn-leaves
  • Which is a synonym of yahoo?
Spell It

Can you spell these 10 commonly misspelled words?

Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.


Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!