Classical Mythology. Often Hydra a water or marsh serpent with nine heads, each of which, if cut off, grew back as two; Hercules killed this serpent by cauterizing the necks as he cut off the heads.
any freshwater polyp of the genus Hydra and related genera, having a cylindrical body with a ring of tentacles surrounding the mouth, and usually living attached to rocks, plants, etc., but also capable of detaching and floating in the water.
a persistent or many-sided problem that presents new obstacles as soon as one aspect is solved.
(initial capital letter) the Sea Serpent, a large southern constellation extending through 90° of the sky, being the longest of all constellations.
any solitary freshwater hydroid coelenterate of the genus Hydra, in which the body is a slender polyp with tentacles around the mouth
a persistent trouble or evil
the hydra of the Irish problem
First recorded in 1325–75; from Latin hydra, from Greek hýdrā “water serpent” (replacing Middle English ydre, from Middle French, from Latin); see otter
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"In 20 years, and despite the resolute efforts of our police officers, gendarmes, judges, teachers and elected officials, the antisemitic hydra has kept advancing," he said.
From Barron's • Feb. 13, 2026
“It’s like a hydra, like a three-headed monster!” she says with a hearty laugh.
From Los Angeles Times • Jan. 22, 2025
This suggests that evolution plays around with these chemical pathways, altering them over the hundreds of millions of years since the hydra and human lineages diverged from each other on the evolutionary tree.
From Scientific American • Jun. 16, 2023
"Greek football is a hydra with many heads. You cut one, others emerge."
From BBC • Feb. 23, 2022
It was almost a good thing that he’d lost his sword, since his gut instinct would’ve been to slash at the heads, and a hydra simply grew two new ones for each one it lost.
From "The Mark of Athena" by Rick Riordan
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.
