jellyfish

noun

jel·​ly·​fish ˈje-lē-ˌfish How to pronounce jellyfish (audio)
1
a
: 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

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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
These pretty pink jellyfish are carnivorous and have stinging tentacles that can reach up to 70 feet long. Meghan Overdeep, Southern Living, 25 Sep. 2025 As with the jellyfish and ctenophores, many of these lose their transparency at depth, becoming red over at least part of their bodies. Literary Hub, 25 Sep. 2025 The Gulf is currently experiencing a bloom of moon jellyfish, which are the pink meanie’s favorite food. Khloe Quill, FOXNews.com, 25 Sep. 2025 At the heart of the park is another immersive extravaganza as footage of seascapes and schools of fish swirls dizzyingly around one of the world’s biggest wraparound screens whilst drones which look like illuminated jellyfish fill the air. Caroline Reid, Forbes.com, 8 Sep. 2025 See All Example Sentences for jellyfish

Word History

First Known Use

1818, in the meaning defined at sense 1a

Time Traveler
The first known use of jellyfish was in 1818

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Cite this Entry

“Jellyfish.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/jellyfish. Accessed 2 Oct. 2025.

Kids Definition

jellyfish

noun
jel·​ly·​fish ˈjel-ē-ˌfish How to pronounce jellyfish (audio)
1
: 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
2
: any of various sea animals that resemble a jellyfish

Medical Definition

jellyfish

noun
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

More from Merriam-Webster on jellyfish

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