jel·​ly·​fish | \ ˈje-lē-ˌfish How to pronounce jellyfish (audio) \

Definition of jellyfish

1a : : the typically free-swimming, bell-shaped, usually sexually-reproducing solitary or colonial form of a cnidarian in which the whorls of tentacles lined with nematocysts arise and hang down from the margin of the nearly transparent, gelatinous bell : medusa especially : a large medusa characteristic of the siphonophores and scyphozoans (such as the sea nettle or box jellyfish)
2 : a person lacking backbone or firmness

Illustration of jellyfish

Illustration of jellyfish

jellyfish 1a

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Synonyms & Antonyms for jellyfish


doormat, namby-pamby, pushover, reed, weakling, wimp



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Examples of jellyfish in a Sentence

a jellyfish who was afraid to tell her boss that her latest brainstorm was just plain bad

Recent Examples on the Web

Invertebrate, soft-bodied creatures like jellyfish and octopus take up seven percent of the world’s biomass (that’s more than 100 times the biomass of humans). Laura Yan, Popular Mechanics, "This Origami Inspired Claw Will Gently Fold Around Jellyfish," 22 July 2018 All sorts of colorful characters swim by—a juvenile jack wedged between the tentacles and bell of a jellyfish for protection, a flying fish harboring a pygmy squid beneath its wing. Laura Mallonee, WIRED, "A Nighttime Underwater Spectacle Off the Coast of the Philippines," 3 Apr. 2018 This type of jellyfish typically feeds on plankton, small fish and other tiny organisms. Jennifer Earl, Fox News, "Giant 'contracting' creature spotted on beach stuns family: 'It's alive'," 18 Sep. 2018 His central discovery was centered on a North American jellyfish, Aequorea victoria, sometimes called the crystal jelly. Harrison Smith, The Seattle Times, "Osamu Shimomura, atomic blast survivor and Nobel-winning chemist, dies at 90," 23 Oct. 2018 Among those species was a giant, tentacle-less jellyfish, which eventually came to be known as Deepstaria enigmatica. National Geographic, "This Mysterious Deep-Sea Jellyfish Looks Like a Plastic Bag," 14 May 2018 The meager calories in jellyfish weren’t the only reason that scientists dismissed them. Carl Zimmer, The Seattle Times, "In the sea, a big appetite for jellyfish," 26 Oct. 2018 While working at Friday Harbor Laboratories, a field station run by the University of Washington, Shimomura discovered a jellyfish protein that allows scientists to trace the movement of cells and proteins. Seattle Times Staff & News Services, The Seattle Times, "This week’s passages," 26 Oct. 2018 Opt for a wetsuit over a traditional bathing suit to stay relatively warmer into September and more protected from the sun, surfboard rash, and even jellyfish. Mara Balagtas, Condé Nast Traveler, "Our 10 Favorite Wetsuits for the Dog Days of Summer," 9 Aug. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'jellyfish.' 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 jellyfish

1818, in the meaning defined at sense 1a

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Statistics for jellyfish

Last Updated

9 Jun 2019

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Time Traveler for jellyfish

The first known use of jellyfish was in 1818

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English Language Learners Definition of jellyfish

: a sea animal that has a very soft body and that can sting


jel·​ly·​fish | \ ˈje-lē-ˌfish How to pronounce jellyfish (audio) \

Kids Definition of jellyfish

: a free-swimming sea animal related to the corals that has a nearly transparent jellylike body shaped like a saucer and tentacles with stinging cells


jel·​ly·​fish | \ ˈjel-ē-ˌfish How to pronounce jellyfish (audio) \

Medical Definition of jellyfish

: a free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells

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More from Merriam-Webster on jellyfish

Rhyming Dictionary: Words that rhyme with jellyfish

Thesaurus: All synonyms and antonyms for jellyfish

Spanish Central: Translation of jellyfish

Nglish: Translation of jellyfish for Spanish Speakers Encyclopedia article about jellyfish

Comments on jellyfish

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


behavior toward others

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