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

• doormat
• namby-pamby
• pushover
• reed
• weakling
• wimp

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

Billie Eilish and Miley Cyrus followed suit with their own twists on the jellyfish. —Anna Cafolla, Vogue, 7 Feb. 2025

The jellyfish cut also sees a drastically shorter layer, but it is cut all the way around the head, while the hime cut only has the front pieces cut. —Hedy Phillips, People.com, 6 Feb. 2025

But unlike jellyfish, which drift and swim in ocean currents, V. velella are at the mercy of the wind. —Margherita Bassi, Smithsonian Magazine, 8 Apr. 2025

For example, green fluorescent protein, which was discovered in jellyfish, is today used in medical studies to illuminate stages of embryological development and to reveal the growth of cancers and other types of cells. —Mindy Weisberger, CNN, 20 Feb. 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