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

Lynne Sladky The nearly 10,000-square-foot (900 square meters) Jellyfish Museum houses roughly 20 unique species of jellyfish found in Florida waters and other parts of the world. — CBS News, 19 Aug. 2026

Swarms of jellyfish are filling the water off Ocean City, Maryland, keeping some beachgoers on shore during the peak summer season. — Daniel Wine, CNN Money, 17 Aug. 2026

Imagine a 350-foot-tall orb that can be transformed into virtually anything, from a harvest moon rising over the Strip to a giant snow globe to a tank of undulating jellyfish. — Condé Nast, Condé Nast Traveler, 15 Aug. 2026

Insects belong to the kingdom Animalia, along with mammals, birds, reptiles, amphibians, fish, octopuses, snails, jellyfish, worms, and many other groups. — Encyclopedia Britannica, 14 Aug. 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