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[hahy-druh] /ˈhaɪ drə/
noun, plural hydras, hydrae
[hahy-dree] /ˈhaɪ dri/ (Show IPA),
for 1–3, genitive hydrae
[hahy-dree] /ˈhaɪ dri/ (Show IPA),
for 4.
(often initial capital letter) Classical Mythology. 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) Astronomy. the Sea Serpent, a large southern constellation extending through 90° of the sky, being the longest of all constellations.
Origin of hydra
1325-75; < Latin < Greek hýdrā water serpent (replacing Middle English ydre < Middle French < L); see otter Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for hydra


noun (pl) -dras, -drae (-driː)
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
Word Origin
C16: from Latin, from Greek hudra water serpent; compare otter


(Greek myth) a monster with nine heads, each of which, when struck off, was replaced by two new ones


noun (Latin genitive) Hydrae (ˈhaɪdriː)
a very long faint constellation lying mainly in the S hemisphere and extending from near Virgo to Cancer
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for hydra

1835, genus name of a freshwater polyp, from Greek Hydra, many-headed Lernaean water serpent slain by Hercules (this sense is attested in English from late 14c.), from hydor (genitive hydatos) "water" (see water (n.1)); related to Sanskrit udrah "aquatic animal" and Old English ottur "otter." Used figuratively for "any multiplicity of evils" [Johnson]. The fabulous beast's heads were said to grown back double when cut off, and the sea creature is said to be so called for its regenerative capabilities.

Online Etymology Dictionary, © 2010 Douglas Harper
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hydra in Science
Plural hydras or hydrae (hī'drē)
See under hydroid.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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