jellyfish

noun

jel·​ly·​fish ˈje-lē-ˌfish 

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)

b

: siphonophore

c

: ctenophore

2

: a person lacking backbone or firmness

Illustration of jellyfish

• jellyfish 1a

Synonyms of jellyfish

• coward
• reed
• mouse
• sheep

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

People should also stay alert to local water conditions, including rip currents and the presence of other marine animals such as jellyfish. — Kelly McGreal, FOXNews.com, 4 July 2026

The lion's mane jellyfish has been spotted along the coast of Massachusetts and other New England states — and in higher-than-normal numbers usually seen at the start of summer, according to local outlets Cape Cod Times, Swampscott Tides and WCVB. — Kimberlee Speakman, PEOPLE, 1 July 2026

The waves will carry the paralyzed bodies to the shore, and even dead jellyfish have been known to sting. — New Atlas, 30 June 2026

If Arenado has made a career of being a thorn in the Giants’ side, Marte has been a jellyfish up their swim shorts this season. — Andrew Baggarly, New York Times, 30 June 2026

Word History

First Known Use

1818, in the meaning defined at sense 1a

Phrases Containing jellyfish

• box jellyfish

Rhymes for jellyfish

• cuttlefish
• sablefish
• bluefish
• catfish
• codfish
• crawfish
• dogfish
• finfish
• flatfish
• goldfish
• groundfish
• kingfish

Kids Definition

jellyfish

noun

jel·​ly·​fish ˈjel-ē-ˌfish 

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 

: 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