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

Sinatra and her colleagues first practiced using the device on fake jellyfish in their lab. Jennifer Leman, Popular Mechanics, "Cool New Robot Can Grab Squishy Fish Without Hurting Them," 28 Aug. 2019 The jellyfish can reach up to roughly 35 inches in diameter, according to the Wildlife Trusts. Ashley Boucher,, "Giant Jellyfish Captured on Video Is Larger Than the Divers Who Spotted It: 'Absolutely Incredible'," 15 July 2019 By mimicking the way a larval jellyfish eats, the robot can capture objects. Matt Simon, WIRED, "This Jellyfish Robot Is Much More Than Just a Good Swimmer," 2 July 2019 There are jellyfish, birds, an octopus, otters, seals and a host of special exhibits. Scott Mcmurren, Anchorage Daily News, "Everyone’s got their go-to Seattle spots. Here are a few more.," 24 Aug. 2019 The room features raw Thai silk, tons of plants, lamps resembling jellyfish, and reclaimed wood from old Thai houses and boats. Janelle Bitker,, "Kin Khao sister restaurant Nari opens in San Francisco with seasonal Thai fare," 8 Aug. 2019 At Maritime Aquarium at Norwalk, kids can see real, grown sharks in a 110,000-gallon habitat, as well as rays, otters, seals, jellyfish, octopi, sea turtles, eels, lobsters, crabs, starfish and other creatures that live in and around the ocean. Susan Dunne,, "Sharks! on exhibit through summer at the Bruce," 3 July 2019 Inside Arizona Mills is an aquarium with 30 displays and more than 5,000 ocean creatures, including clown fish, sea turtles, sharks, jellyfish, rays, octopus and seahorses. Arizona Republic, azcentral, "Summer in Arizona: Locals share 100 fun ways to survive the 100-degree heat in Phoenix," 1 July 2019 During another dive, a large jellyfish ran into my face in relatively deep depth. Georgia Frances King, Quartz, "The world’s most famous explorers on how they handle high-stress situations," 14 Aug. 2019

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

15 Sep 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).


authorized for issue (as a bond)

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