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

Researchers found that the jellyfish, which host photosynthetic algae, are active during the day, sleep mainly at night, and even take midday naps, much like some humans do after lunch. —New Atlas, 24 Jan. 2026

Though the entire look evoked a jellyfish, small white butterflies could also be glimpsed on the athlete’s apparel and accessories — a reference to Osaka’s 2021 Australian Open tennis match when the athlete moved a butterfly that landed on her face off the court. —Julia Teti, Footwear News, 20 Jan. 2026

Australia's infamous for the variety of ways its wildlife can kill you — deadly snakes, spiders, and jellyfish. —Holly Williams, CBS News, 19 Jan. 2026

The Oklahoma Aquarium is the biggest in the state at 72,000 square feet, and features sharks, jellyfish, alligator gars, as well as beavers and otters. —Isa Almeida, Oklahoman, 15 Jan. 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