*ydra*

n. a genus of snapping turtles.
Syn. -- genus Chelydra. [ WordNet 1.5 ]

n. 1. a chemical substance (CCl3.CH(OH)2) which is a hydrate of trichloroacetaldehyde. It crystallizes as white monoclinic plates, obtained by treating chloral with water. It produces sleep when taken internally or hypodermically, and is used in medicine as a hypnotic and sedative; -- called also chloral It may be habit-forming, and is a controlled substance listed in the U. S. Code of Federal Regulations. It is sometimes used to render a person unconscious for illegal or nefarious purposes, and in this use, a concentrated solution is one of the agents called knockout drops. [ PJC ]

n. [ L. from Gr. &unr_;; &unr_; to steal, conceal + &unr_; water. ] A water clock; a contrivance for measuring time by the graduated flow of a liquid, as of water, through a small aperture. See Illust. in Appendix. [ 1913 Webster ]

n. [ Gr. kry`os cold + E. hydrate. ] (Chem.) A substance, as salt, ammonium chloride, etc., which crystallizes with water of crystallization only at low temperatures, or below the freezing point of water. F. Guthrie. [ 1913 Webster ]

v. t. To deprive of water; to render free from water; as, to dehydrate alcohol; to dehydrate food for preservation. [ 1913 Webster ]

v. i. 1. to lose water or moisture. [ PJC ]

2. to lose sufficent water to cause physiological distress; -- of living organisms; as, victims trapped in the earthquake rubble may dehydrate if not found quickly. [ PJC ]

adj. 1. thoroughly dried out.
Syn. -- desiccated, dried-out. [ WordNet 1.5 ]

2. suffering from fluid deprivation; as, to become deydrated from overexertion on a hot day. [ WordNet 1.5 ]

n. (Chem.) The act or process of freeing from water; also, the condition of a body from which the water has been removed. [ 1913 Webster ]

n. an upright hydrant that can supply large volumes of water to use in fighting a fire. They are commonly placed at intervals at the street edge of a sidewalk, spaced for convenience in suppressing fires in towns.
Syn. -- fireplug, plug. [ WordNet 1.5 +PJC ]

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]

prop. n. A natural family of plants including the hydrangeas, sometimes included in the family Saxifragaceae.
Syn. -- family Hydrangeaceae, hydrangea family. [ WordNet 1.5 ]

n. [ Gr. &unr_; to irrigate, fr. "y`dwr water. See Hydra.] A discharge pipe with a valve and spout at which water may be drawn from the mains of waterworks; a water plug. [1913 Webster]

n. [ Hydra + Gr. &unr_; a flower. ] (Zool.) One of the nutritive zooids of a hydroid colony. Also applied to the proboscis or manubrium of a hydroid medusa. See Illust. of Hydroidea. [ 1913 Webster ]

n. [ Hydrargyrum + chloride. ] (Chem.) A compound of the bichloride of mercury with another chloride. [ Obs. ] [ 1913 Webster ]

a. Of or pertaining to mercury; containing, or impregnated with, mercury. [ R. ] [ 1913 Webster ]

n. (Med.) A diseased condition produced by poisoning with hydrargyrum, or mercury; mercurialism. [ 1913 Webster ]

n. [ NL., fr. L. hydrargyrus, Gr. "ydra`rgyros; "y`dwr water + 'a`rgyros silver. ] (Chem.) Quicksilver; mercury. [ 1913 Webster ]

‖n. [ NL. See Hydro-, 1, and Arthrosis. ] (Med.) An effusion of watery liquid into the cavity of a joint. [ 1913 Webster ]

n. (Chem.) An alkaloid, found in the rootstock of the golden seal (Hydrastis Canadensis), and extracted as a bitter, white, crystalline substance. It is used as a tonic and febrifuge. [ 1913 Webster ]

a. Dipped in the gall of the fabulous hydra; poisonous; deadly. Cowper. [ 1913 Webster ]

n. [ Gr. "y`dwr water: cf. F. hydrate.] (Chem.) (a) A compound formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts. (b) A substance which does not contain water as such, but has its constituents (hydrogen, oxygen, hydroxyl) so arranged that water may be eliminated; hence, a derivative of, or compound with, hydroxyl; hydroxide; as, ethyl hydrate, or common alcohol; calcium hydrate, or slaked lime. [1913 Webster]

v. t. [ imp. & p. p. Hydrated p. pr. & vb. n. Hydrating ] To form into a hydrate; to combine with water. [ 1913 Webster ]

a. Formed into a hydrate; combined with water. [ 1913 Webster ]

n. (Chem.) The act of becoming, or state of being, a hydrate. [ 1913 Webster ]

Water of hydration (Chem.), water chemically combined with some substance to form a hydrate; -- distinguished from water of crystallization. [ 1913 Webster ]

a. [ F. hydraulique, L. hydraulicus, fr. Gr. &unr_;, &unr_;, a water organ; "y`dwr water + &unr_; flute, pipe. See Hydra.] Of or pertaining to hydraulics, or to fluids in motion; conveying, or acting by, water; as, an hydraulic clock, crane, or dock. [1913 Webster]

Hydraulic accumulator, an accumulator for hydraulic machinery of any kind. See Accumulator, 2. --
Hydraulic brake, a cataract. See Cataract, 3. --
Hydraulic cement, a cement or mortar made of hydraulic lime, which will harden under water. --
Hydraulic elevator, a lift operated by the weight or pressure of water. --
Hydraulic jack. See under Jack. --
Hydraulic lime, quicklime obtained from hydraulic limestone, and used for cementing under water, etc. --
Hydraulic limestone, a limestone which contains some clay, and which yields a quicklime that will set, or form a firm, strong mass, under water. --
Hydraulic main (Gas Works), a horizontal pipe containing water at the bottom into which the ends of the pipes from the retorts dip, for passing the gas through water in order to remove ammonia. --
Hydraulic mining, a system of mining in which the force of a jet of water is used to wash down a bank of gold-bearing gravel or earth. [Pacific Coast] --
Hydraulic press, a hydrostatic press. See under Hydrostatic. --
Hydraulic propeller, a device for propelling ships by means of a stream of water ejected under water rearward from the ship. --
Hydraulic ram, a machine for raising water by means of the energy of the moving water of which a portion is to be raised. When the rush of water through the main pipe d shuts the valve at a, the momentum of the current thus suddenly checked forces part of it into the air chamber b, and up the pipe c, its return being prevented by a valve at the entrance to the air chamber, while the dropping of the valve a by its own weight allows another rush through the main pipe, and so on alternately. --
Hydraulic valve. (Mach.) (a) A valve for regulating the distribution of water in the cylinders of hydraulic elevators, cranes, etc. (b) (Gas Works) An inverted cup with a partition dipping into water, for opening or closing communication between two gas mains, the open ends of which protrude about the water. [1913 Webster]

a. Hydraulic. [ 1913 Webster ]

n. [ NL. See Hydraulic. ] (Mus.) An ancient musical instrument played by the action of water; a water organ. [ Written also hydraulis. ] [ 1913 Webster ]

n. [ Cf. F. hydraulique. ] That branch of science, or of engineering, which treats of fluids in motion, especially of water, its action in rivers and canals, the works and machinery for conducting or raising it, its use as a prime mover, and the like. [ 1913 Webster ]

☞ As a science, hydraulics includes hydrodynamics, or the principles of mechanics applicable to the motion of water; as a branch of engineering, it consists in the practical application of the mechanics of fluids to the control and management of water with reference to the wants of man, including canals, waterworks, hydraulic machines, pumps, water wheels, etc. Some writers treat hydraulics and hydrostatics as subdivisions of hydrodynamics. [ 1913 Webster ]

n. [ Hydr- + azo- + -ine. ] (Chem.) Any one of a series of nitrogenous bases, resembling the amines and produced by the reduction of certain nitroso and diazo compounds; as, methyl hydrazine, phenyl hydrazine, etc. They are derivatives of hydrazine proper, H2N.NH2, which is a doubled amido group, recently (1887) isolated as a stable, colorless gas, with a peculiar, irritating odor. As a base it forms distinct salts. Called also diamide, amidogen, (or more properly diamidogen), etc. [ 1913 Webster ]

a. [ Stereo- + hydraulic. ] Pertaining to, or designating, a kind of hydraulic press; resembling such a press in action or principle. [ 1913 Webster ]

Sterhydraulic press, an hydraulic press producing pressure or motion by the introduction of a solid substance (as a long rod, or a cord wound on a roller) into a cylinder previously filled with a liquid. [ 1913 Webster ]

n. (Chem.) A compound, analogous to a hydrate, regarded as a salt of sulphydric acid, or as a derivative of hydrogen sulphide in which one half of the hydrogen is replaced by a base (as potassium sulphydrate, KSH), or as a hydrate in which the oxygen has been wholly or partially replaced by sulphur. [ 1913 Webster ]