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

Among the new characters are the Wind Traders, a new group of Na’vi who travel across Pandora on giant airships that look like jellyfish. —Jazz Tangcay, Variety, 17 Dec. 2025

The foam unit kept the Adistar Cushion 3’s general shape but expanded it in height and width, with curved grooves along the sides that Adidas has linked to the fluid form of a jellyfish. —Maggie Clancy, Footwear News, 16 Dec. 2025

The Texas State Aquarium is a surefire win time after time, as the young and young at heart can explore numerous exhibits with jellyfish, sharks, eels, and touch tanks to get up close and personal. —Amanda Ogle, Travel + Leisure, 7 Dec. 2025

According to the Florida Department of Environmental Protection, lifeguards will fly a purple flag on their beaches to let people know of stinging wildlife, which includes stingrays, jellyfish and the Portuguese man o' war. —Hunter Geisel, CBS News, 3 Dec. 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