n.; pl. E. Hydras L. Hydræ [ L. hydra, Gr. "y`dra; akin to "y`dwr water. See Otter the animal, Water. ] 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. [ 1913 Webster ]

Gorgons, and Hydras, and Chimeras dire. Milton. [ 1913 Webster ]

2. Hence: A multifarious evil, or an evil having many sources; not to be overcome by a single effort. [ 1913 Webster ]

3. (Zool.) Any small fresh-water hydroid of the genus Hydra, usually found attached to sticks, stones, etc., by a basal sucker. [ 1913 Webster ]

☞ 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. [ 1913 Webster ]

4. (Astron.) A southern constellation of great length lying southerly from Cancer, Leo, and Virgo. [ 1913 Webster ]

n. [ Hydr- + arachnid. ] (Zool.) An aquatic mite of the genus Hydrachna. The hydrachnids, while young, are parasitic on fresh-water mussels. [ 1913 Webster ]

n. [ Hydr- + acid: cf. F. hydracide. ] (Chem.) An acid containing hydrogen; -- sometimes applied to distinguish acids like hydrochloric, hydrofluoric, and the like, which contain no oxygen, from the oxygen acids or oxacids. See Acid. [ 1913 Webster ]

a. [ Hydr- + acrylic. ] (Chem.) Pertaining to, or designating, an isomeric variety of lactic acid that breaks down into acrylic acid and water. [ 1913 Webster ]

n. [ See Hydra, and Actinia. ] (Zool.) Any species or marine hydroids, of the genus Hydractinia and allied genera. These hydroids form, by their rootstalks, a firm, chitinous coating on shells and stones, and esp. on spiral shells occupied by hermit crabs. See Illust. of Athecata. [ 1913 Webster ]

‖n. [ NL., fr. Gr. "y`dwr water + a"i^ma blood. ] (Med.) An abnormally watery state of the blood; anæmia. [ 1913 Webster ]

a. [ L. hydragogus conveying off water, Gr. &unr_;; "y`dwr water + &unr_; to lead: cf. F. hydragogue.] (Med.) Causing a discharge of water; expelling serum effused into any part of the body, as in dropsy. -- n. A hydragogue medicine, usually a cathartic or diuretic. [1913 Webster]

n. [ Hydr- + -amide. ] (Chem.) One of a group of crystalline bodies produced by the action of ammonia on certain aldehydes. [ 1913 Webster ]

n. [ Hydroxyl + amine. ] (Chem.) One of a series of artificial, organic bases, usually produced as thick viscous liquids by the action of ammonia on ethylene oxide. They have the properties both of alcohol and amines. [ 1913 Webster ]

peop. n. [ NL., fr. Gr. "y`dwr water + &unr_; vessel, capsule: cf. F. hydrangée.] (Bot.) A genus of shrubby plants bearing opposite leaves and large heads of showy flowers, white, or of various colors. Hydrangea hortensis, the common garden species, is a native of China or Japan. [1913 Webster]