Hydantoin Hy·dan"to·in noun [ Hyd rogen + all antion .] (Chemistry) A derivative of urea, C ₃ H ₄ N ₂ O ₂ , obtained from allantion, as a white, crystalline substance, with a sweetish taste; -- called also glycolyl urea .

Hydatid Hy"da·tid noun [ Greek ..., ..., a watery vesicle under the upper eyelid, from "y`dwr , "y`datos , water: confer French hydatide .] (Zoology) A membranous sac or bladder filled with a pellucid fluid, found in various parts of the bodies of animals, but unconnected with the tissues. It is usually formed by parasitic worms, esp. by larval tapeworms, as Echinococcus and Cœnurus. See these words in the Vocabulary.

Hydatid of Morgagni (Anat.) , one of the small pedunculated bodies found between the testicle and the head of the epididymis, and supposed to be a remnant of the Müllerian duct.

Hydatiform Hy·dat"i·form adjective [ Hydatid + -form .] Resembling a hydatid.

Hydatoid Hy"da·toid adjective [ Greek "y`dwr , "y`datos , water + -oid .] (Anat.) Resembling water; watery; aqueous; hyaloid.

Hydr- Hy"dr- See under Hydro- .

Hydra Hy"dra noun ; plural English Hydras , Latin Hydræ . [ Latin hydra , Greek "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.

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. (Zoology) Any small fresh-water hydroid of the genus Hydra , usually found attached to sticks, stones, etc., by a basal sucker.

» 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.

Hydra-tainted Hy"dra-taint`ed adjective Dipped in the gall of the fabulous hydra; poisonous; deadly. Cowper.

Hydrachnid Hy·drach"nid noun [ Hydr- + ar achnid .] (Zoology) An aquatic mite of the genus Hydrachna . The hydrachnids, while young, are parasitic on fresh-water mussels.

Hydracid Hy·drac"id noun [ Hydr- + acid : confer French hydracide .] (Chemistry) 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 .

Hydracrylic Hy`dra·cryl"ic adjective [ Hydr- + acrylic .] (Chemistry) Pertaining to, or designating, an isomeric variety of lactic acid that breaks down into acrylic acid and water.

Hydractinian Hy`drac·tin"i·an noun [ See Hydra , and Actinia .] (Zoology) 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 .

Hydragogue Hy"dra·gogue adjective [ Latin hydragogus conveying off water, Greek ...; "y`dwr water + ... to lead: confer French hydragogue .] (Medicine) Causing a discharge of water; expelling serum effused into any part of the body, as in dropsy. -- noun A hydragogue medicine, usually a cathartic or diuretic.

Hydramide Hy·dram"ide noun [ Hydr- + -amide .] (Chemistry) One of a group of crystalline bodies produced by the action of ammonia on certain aldehydes.

Hydramine Hy·dram"ine noun [ Hydr oxyl + amine .] (Chemistry) 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.

Hydrangea Hy·dran"ge·a noun [ New Latin , from Greek "y`dwr water + ... vessel, capsule: confer French hydrangée .] (Botany) A genus of shrubby plants bearing opposite leaves and large heads of showy flowers, white, or of various colors. H. hortensis , the common garden species, is a native of China or Japan.

Hydrant Hy"drant noun [ Greek ... to irrigate, from "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.

Hydranth Hy"dranth noun [ Hydra + Greek ... a flower.] (Zoology) One of the nutritive zooids of a hydroid colony. Also applied to the proboscis or manubrium of a hydroid medusa. See Illust. of Hydroidea .

Hydrargochloride Hy·drar"go·chlo"ride noun [ Hydrarg yrum + chloride .] (Chemistry) A compound of the bichloride of mercury with another chloride. [ Obsolete]

Hydrargyrate Hy·drar"gy·rate adjective Of or pertaining to mercury; containing, or impregnated with, mercury. [ R.]

Hydrargyrism Hy·drar"gy·rism noun (Medicine) A diseased condition produced by poisoning with hydrargyrum, or mercury; mercurialism.

Hydrargyrum Hy·drar"gy·rum (-rŭm) noun [ New Latin , from Latin hydrargyrus , Greek "ydra`rgyros ; "y`dwr water + 'a`rgyros silver.] (Chemistry) Quicksilver; mercury.

Hydrarthrosis Hy`drar·thro"sis noun [ New Latin See Hydro- , 1, and Arthrosis .] (Medicine) An effusion of watery liquid into the cavity of a joint.

Hydrastine Hy·dras"tine noun (Chemistry) 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.

Hydrate Hy"drate noun [ Greek "y`dwr water: confer French hydrate .] (Chemistry) (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.

Hydrate Hy"drate transitive verb [ imperfect & past participle Hydrated ; present participle & verbal noun Hydrating .] To form into a hydrate; to combine with water.

Hydrated Hy"dra·ted adjective Formed into a hydrate; combined with water.

Hydration Hy·dra"tion noun (Chemistry) The act of becoming, or state of being, a hydrate.

Water of hydration (Chemistry) , water chemically combined with some substance to form a hydrate; -- distinguished from water of crystallization .

Hydraulic Hy·drau"lic adjective [ French hydraulique , Latin hydraulicus , from Greek ..., ..., a water organ; "y`dwr water + ... 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.

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 . (Machinery) (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.

Hydraulical Hy·drau"lic·al adjective Hydraulic.

Hydraulicon Hy·drau"li·con noun [ New Latin See Hydraulic .] (Mus.) An ancient musical instrument played by the action of water; a water organ. [ Written also hydraulis .]

Hydraulics Hy·drau"lics noun [ Confer French 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.

» 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.

Hydrazine Hy"dra·zine noun [ Hydr- + azo- + -ine .] (Chemistry) 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, H ₂ N.NH ₂ , 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.

Hydrencephsloid Hy"dren·ceph"s·loid adjective [ Hydrencephal us + -oid .] (Medicine) Same as Hydrocephaloid .

Hydria Hy"dri·a noun [ Latin , from Greek ....] (Gr. Antiq.) A water jar; esp., one with a large rounded body, a small neck, and three handles. Some of the most beautiful Greek vases are of this form.

Hydriad Hy"dri·ad noun [ Greek ..., ..., of the water, from "y`dwr water.] (Myth.) A water nymph.

Hydric Hy"dric adjective [ From Hydrogen .] (Chemistry) Pertaining to, or containing, hydrogen; as, hydric oxide.

Hydric dioxide . (Chemistry) See Hydrogen dioxide , under Hydrogen . -- Hydric oxide (Chemistry) , water. -- Hydric sulphate (Chemistry) , hydrogen sulphate or sulphuric acid.

Hydride Hy"dride noun [ Hydr- + ide .] (Chemistry) A compound of the binary type, in which hydrogen is united with some other element.

Hydriform Hy"dri·form adjective [ Hydra + -form .] (Zoology) Having the form or structure of a hydra.

Hydrina Hy·dri"na noun plural [ New Latin See Hydra .] (Zoology) The group of hydroids to which the fresh-water hydras belong.

Hydriodate Hy·dri"o·date noun [ Confer French hydriodate .] (Zoology) Same as Hydriodide .

Hydriodic Hy`dri·od"ic adjective [ Hydr- + iodic : confer French hydriodique .] (Chemistry) Pertaining to, or derived from, hydrogen and iodine; -- said of an acid produced by the combination of these elements.

Hydriodic acid (Chemistry) , a pungent, colorless gas, HI, usually prepared as a solution in water. It is strong reducing agent. Called also hydrogen iodide .

Hydriodide Hy·dri"o·dide noun (Chemistry) A compound of hydriodic acid with a base; -- distinguished from an iodide , in which only the iodine combines with the base.

Hydro Hy"dro noun A hydro- aëroplane.

Hydro-, Hydr- Hy"dro-, Hy"dr- 1. A combining form from Greek ..., ..., water (see Hydra ).

2. (Chemistry) A combining form of hydrogen , indicating hydrogen as an ingredient , as hydro chloric; or a reduction product obtained by hydrogen , as hydro quinone.

Hydro-aëroplane Hy"dro-a"ër·o·plane` (Aëronautics) An aëroplane with a boatlike or other understructure that enables it to travel on, or to rise from the surface of, a body of water by its own motive power.

Hydro-electric Hy`dro-e·lec"tric adjective [ Hydro- , 1 + electric .] Pertaining to, employed in, or produced by, the evolution of electricity by means of a battery in which water or steam is used.

Hydro-electric machine (Physics) , an apparatus invented by Sir William Armstrong of England for generating electricity by the escape of high-pressure steam from a series of jets connected with a strong boiler, in which the steam is produced.

Hydro-extractor Hy`dro-ex·tract"or noun [ Hydro- , 1 + extractor .] An apparatus for drying anything, as yarn, cloth, sugar, etc., by centrifugal force; a centrifugal.

Hydrobarometer Hy`dro·ba·rom"e·ter noun [ Hydro- , 1 + barometer .] An instrument for determining the depth of the sea water by its pressure.

Hydrobilirubin Hy`dro·bil`i·ru"bin noun [ Hydro- , 2 + bilirubin .] (Physiol. Chem.) A body formed from bilirubin, identical with urobilin.

Hydrobiplane Hy"dro·bi"plane noun A hydro- aëroplane having two supporting planes.

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