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

Comb jellies are an ancient animal lineage with a distinct evolutionary history, and despite their similar appearance, they are not closely related to true jellyfish. —Scott Travers, Forbes, 13 Dec. 2024

They are made up of individual polyps – related to jellyfish and anemones – that group together, making use of calcium and carbonate ions to create a calcium carbonate skeleton. —Sean Mowbray, Discover Magazine, 12 Dec. 2024

For starters, the planet’s magnetic field lines look like the head and arms of a flailing jellyfish. —Shi En Kim, Smithsonian Magazine, 5 Nov. 2024

Nudibranchs primarily eat jellyfish, anemones, sponges and other aquatic invertebrates—but some are cannibalistic. —Sarah Kuta, Smithsonian Magazine, 20 Nov. 2024

Word History

First Known Use

1818, in the meaning defined at sense 1a

Phrases Containing jellyfish

• box jellyfish

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