Hy·dra n.; pl. E. Hydras L. Hydræ
 1. Class. Myth. A serpent or monster in the lake or marsh of Lerna, in the Peloponnesus, represented as having many heads, one of which, when cut off, was immediately succeeded by two others, unless the wound was cauterized. It was slain by Hercules. Hence, a terrible monster.
    Gorgons, and Hydras, and Chimeras dire.   --Milton.
 2. Hence: A multifarious evil, or an evil having many sources; not to be overcome by a single effort.
 3. Zool. Any small fresh-water hydroid of the genus Hydra, usually found attached to sticks, stones, etc., by a basal sucker.
 Note: ☞ The body is a simple tube, having a mouth at one extremity, surrounded by a circle of tentacles with which it captures its prey. Young hydras bud out from the sides of the older ones, but soon become detached and are then like their parent. Hydras are remarkable for their power of repairing injuries; for if the body be divided in pieces, each piece will grow into a complete hydra, to which fact the name alludes. The zooids or hydranths of marine hydroids are sometimes called hydras.
 4. Astron. A southern constellation of great length lying southerly from Cancer, Leo, and Virgo.
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