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.
Watch huge jellyfish make appearance on Maine beach Jellyfish warnings issued Several coastal communities in Maine issued a jellyfish warning as there has been an increase in sightings of lion’s mane and moon jellyfish, according to local station Fox 23 Maine. Julia Gomez, USA Today, 27 June 2025 In addition, lifeguards often have access to real-time information about water quality, tides, jellyfish blooms and other hazards that the average beachgoer wouldn’t otherwise be aware of. Scott Travers, Forbes.com, 21 June 2025 The room, decorated with an under-the-sea theme, had a balloon arch decked out with streamers meant to look like jellyfish and a cloud of clear balloons mimicking ocean bubbles. Lydia McFarlane, Miami Herald, 12 June 2025 Cocoa Kayaking and Adventure Kayak of Cocoa Beach lead a variety of expeditions, including mangrove tours through the Thousand Islands and nighttime trips to see bioluminescent jellyfish. Lisa Cericola, Southern Living, 8 June 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 8 Jul. 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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