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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Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Samar shares the popular view that for every senior official "they've reportedly assigned three to seven successors. Like a hydra - you cut one head off, another grows back. They won't surrender any time soon."
From BBC ● Mar. 25, 2026
"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
Despite my efforts at hogging the window, I feel myself getting shoved aside as Jude squeezes her head and then her shoulders out beside mine until we’re a two-headed hydra.
From "I'll Give You the Sun" by Jandy Nelson
Their Catapult Hydra protocol is proprietary but tested.
From Salon ● Feb. 12, 2026
The supernova is located in the galaxy NGC 3621, in the direction of the constellation Hydra, approximately 22 million light-years away.
From Science Daily ● Nov. 16, 2025
The Marvel universe more recently used the Nazi-like Hydra organization as a multiheaded big bad.
From New York Times ● Jun. 19, 2024
He started gathering intelligence on the Asian buyers, in an investigation called Operation Hydra.
From BBC ● Aug. 15, 2023
But even Tyson couldn’t fend off the Hydra forever.
From "The Sea of Monsters" by Rick Riordan
On the topic of aging, Earth does actually have organisms that are functionally immortal, such as hydras.
From Scientific American ● May 28, 2023
"Online services are like hydras, if you fix one problem, another one often emerges," James Mickens, a professor of computer science at Harvard, explains in a statement.
From BBC ● Sep. 9, 2021
Everyone in New York has heard about co-op boards that proved to be the most persnickety of the many many-headed hydras exerting authority over daily life.
From New York Times ● May 8, 2016
The name van Leeuwenhoek gave them was “polyps,” though they would eventually be commonly known as hydras.
From Salon ● Jan. 17, 2016
There were miniature lions, pigs, dragons, hydras, even a teeny Minotaur in a little Minotaur diaper.
From "The Last Olympian" by Rick Riordan
EX Hydrae exists in a binary system alongside a normal main sequence star.
From Science Daily ● Jan. 8, 2026
In EX Hydrae, the magnetic field is not strong enough to direct all incoming material onto the star's magnetic poles.
From Science Daily ● Jan. 8, 2026
The infalling matter collides with other material bound to the white dwarf, forming tall columns of hot gas that emit intense X-rays, making systems like EX Hydrae ideal targets for IXPE.
From Science Daily ● Jan. 8, 2026
The mission's ability to measure the polarization of X-rays allowed astronomers to closely examine EX Hydrae, a type of system known as an intermediate polar.
From Science Daily ● Jan. 8, 2026
You saw that big Beta Hydrae orrery at Kankad's observatory.
From Uller Uprising by Clark, John D.
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.
