jellyfish
Americannoun
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any of various marine coelenterates of a soft, gelatinous structure, especially one with an umbrellalike body and long, trailing tentacles; medusa.
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Informal. a person without strong resolve or stamina; an indecisive or weak person.
noun
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any marine medusoid coelenterate of the class Scyphozoa, having a gelatinous umbrella-shaped body with trailing tentacles
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any other medusoid coelenterate
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informal a weak indecisive person
Etymology
Origin of jellyfish
1700–10; 1910–15 jellyfish for def. 2; jelly + fish
Explanation
A jellyfish is a marine animal with long tentacles that hang down from a bell-shaped body. Many jellyfish are nearly transparent. Jellyfish may look like they're made of jelly, but their bodies are actually 95 percent water. These umbrella-shaped creatures look graceful floating in the water, but they collapse into a flat blob on land. Jellyfish don't have organs, just a simple nervous system and three layers including the elastic, jelly-like mesoglea that gives them their name. In the 19th century, it became fairly common to call a weak person a jellyfish, a figurative usage that's still around today.
Vocabulary lists containing jellyfish
Reef Awareness Day, List 1
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Marine Biology - Introductory
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Marine Biology - Middle School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Researchers at the University of Waterloo have identified the farthest jellyfish galaxy ever observed.
From Science Daily • Mar. 3, 2026
Among the species discovered were ancient relatives of worms, sponges and jellyfish.
From Barron's • Jan. 28, 2026
The 28-year-old revealed her outfit was originally inspired by a jellyfish, which she saw in a book while reading to her two-year-old daughter.
From BBC • Jan. 20, 2026
I spent several hours spellbound by the aquarium—don’t miss the octopus and jellyfish tanks—and the museum of the world’s oceans.
From The Wall Street Journal • Jan. 10, 2026
It left behind a vast expanse of mud, seaweed, shells, and the occasional, very unlucky jellyfish.
From "Ugly" by Robert Hoge
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
