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
Other Word Forms
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.
Here you might spy a lion’s mane jellyfish, whose stinging tentacles have been known to grow more than 100 feet, longer than the length of a basketball court.
From The Wall Street Journal • May 22, 2026
It's a sign of how a weird, underground act that sang about aliens and jellyfish have become extraordinarily influential proponents of queer culture and alternative rock.
From BBC • Mar. 17, 2026
These included mammals, reptiles, fish, jellyfish, and shrimp collected by Darwin and other naturalists during early scientific expeditions.
From Science Daily • Mar. 5, 2026
When they open them, a seascape galaxy of stars appears -- the bluish-white flashes of creatures from plankton and jellyfish to shrimp and fish responding to the sub lights.
From Barron's • Jan. 26, 2026
The text explained that the jar held something called an Irukandji jellyfish, whose venom is among the most dangerous in the world.
From "The Thing About Jellyfish" by Ali Benjamin
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.
