hydra

[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.
1.
(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.
2.
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.
3.
a persistent or many-sided problem that presents new obstacles as soon as one aspect is solved.
4.
(initial capital letter) Astronomy. the Sea Serpent, a large southern constellation extending through 90° of the sky, being the longest of all constellations.
Origin
1325-75; < Latin < Greek hýdrā water serpent (replacing Middle English ydre < Middle French < L); see otter
Examples from the web for hydra
  • It was later revealed that the creature originated from the hydra system.
British Dictionary definitions for hydra

hydra

/ˈhaɪdrə/
noun (pl) -dras, -drae (-driː)
1.
any solitary freshwater hydroid coelenterate of the genus Hydra, in which the body is a slender polyp with tentacles around the mouth
2.
a persistent trouble or evil: the hydra of the Irish problem
Word Origin
C16: from Latin, from Greek hudra water serpent; compare otter

Hydra1

/ˈhaɪdrə/
noun
1.
(Greek myth) a monster with nine heads, each of which, when struck off, was replaced by two new ones

Hydra2

/ˈhaɪdrə/
noun (Latin genitive) Hydrae (ˈhaɪdriː)
1.
a very long faint constellation lying mainly in the S hemisphere and extending from near Virgo to Cancer
Word Origin and History for hydra
n.

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.

hydra in Science
hydra
  (hī'drə)   
Plural hydras or hydrae (hī'drē)
See under hydroid.