jel·​ly·​fish ˈje-lē-ˌfish How to pronounce jellyfish (audio)
: 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)
: a person lacking backbone or firmness

Illustration of jellyfish

Illustration of jellyfish
  • jellyfish 1a

Example Sentences

a jellyfish who was afraid to tell her boss that her latest brainstorm was just plain bad
Recent Examples on the Web In nature, transparency is largely reserved for fully aquatic creatures such as eel larvae and gelatinous jellyfish. Byjack Tamisiea,, 22 Dec. 2022 The effect, which resembled that of a space jellyfish, was captured by multiple people on social media, including a few beautiful photos shared by NCSpaceOps on Twitter. Joshua Hawkins, BGR, 19 Dec. 2022 The disruptive designer, who helms M51 Concepts, has just unveiled a new megayacht concept that features two multi-story jellyfish aquariums inside to give seafarers a prime view of the ocean’s wonders. Rachel Cormack, Robb Report, 12 Dec. 2022 Giant jellyfish could be seen from the helicopter U.S. Coast Guard Lt. Katy Caraway was flying Sunday. María Luisa Paúl, Washington Post, 14 Oct. 2022 More research is needed to further understand this jellyfish’s aging process. Margaret Osborne, Smithsonian Magazine, 6 Sep. 2022 There are nymphs with glass-and-shell bustiers, organza jellyfish, and a gown covered in iridescent scales, embroidered with crystals, costume diamonds, feathers, and horsehair. Tara Gonzalez, Harper's BAZAAR, 18 Nov. 2022 In Nussbaum’s view, all mammals fall within this category; so too do bony fish and birds; insects can go either way; corals, jellyfish, and sponges don’t qualify. Sasha Frere-jones, Harper’s Magazine , 9 Nov. 2022 They can also be made with ‘soft’ materials and thus can replicate important mechanical qualities—one type can ‘swim’ like a jellyfish, and another has a gripping ability that can precisely pick and place miniature objects. IEEE Spectrum, 23 Jan. 2023 See More

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.

Word History

First Known Use

1818, in the meaning defined at sense 1a

Time Traveler
The first known use of jellyfish was in 1818

Dictionary Entries Near jellyfish

Cite this Entry

“Jellyfish.” Dictionary, Merriam-Webster, Accessed 27 Mar. 2023.

Kids Definition


jel·​ly·​fish ˈjel-ē-ˌfish How to pronounce jellyfish (audio)
: any of numerous free-swimming coelenterate animals that reproduce sexually and have a jellylike, saucer-shaped, and usually nearly transparent body and tentacles with stinging cells
: any of various sea animals that resemble a jellyfish

Medical Definition


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