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

• 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

Gloucester, Massachusetts, reminded beachgoers to stay safe around jellyfish in mid-July. —Leo Schwartz, Fortune, 6 Aug. 2025

The series features innovative design elements, including spaceships inspired by jellyfish that are conceived as living, organic vessels rather than traditional metal craft. —Naman Ramachandran, Variety, 28 July 2025

Plankton and jellyfish are basically drafting right along with the current instead of swimming in it. —Laura Baisas, Popular Science, 17 July 2025

The species is the largest of the 200 species of jellyfish in the world. —Mike Stunson, Miami Herald, 24 June 2025

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