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

Astrophotographer Ogetay Kayali has captured a nebula resembling a jellyfish — or possibly a brain, depending on your perspective — shining 5,000 light-years from Earth near the bright star Propus, which represents one foot of a mythological twin represented in the constellation Gemini. —Anthony Wood, Space.com, 7 Mar. 2026

The species discovered include ancient relatives of worms, sponges and jellyfish. —Hanna Wickes, Charlotte Observer, 27 Feb. 2026

What Lived 512 Million Years Ago The species discovered include ancient relatives of worms, sponges and jellyfish. —Hanna Wickes, Kansas City Star, 27 Feb. 2026

Visitors can explore an underwater world that includes an ocean tunnel, sea turtle rescue center, an interactive touch pool, jellyfish, colorful tropical fish, seahorse displays and more. —Alyson Rodriguez, Dallas Morning News, 25 Feb. 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