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

The jellyfish-like creatures began washing up on Central Coast beaches in mid-April, The Tribune previously reported. —Stephanie Zappelli, Sacbee.com, 23 Apr. 2026

SeaWorld likens the experience to the LED room in its Jewels of the Sea attraction that brings to life various shapes and sizes of jellyfish. —Lori Weisberg, San Diego Union-Tribune, 23 Apr. 2026

Irukandji jellyfish is reportedly a type of box jellyfish. —Gabrielle Rockson, PEOPLE, 22 Apr. 2026

The aquarium features hundreds of thousands of gallons of water and dozens of habitats filled with nearly 8,000 animals, including sharks, sea turtles, stingrays and jellyfish. —Taylor Haught, Kansas City Star, 21 Apr. 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