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hydrofoil a winglike structure that is attached to a vessel to raise its hull above the water when the vessel is moving and thus to increase its speed. [2 definitions]
hydrogen a chemical element that contains one proton in each nucleus and that occurs naturally in many compounds such as water, acids, petroleum hydrocarbons, and carbohydrates, and in pure form as a highly flammable, lighter-than-air gas used in many industrial applications, such as the hydrogenation of fats and oils. (symbol: H) (Cf. deuterium, protium, tritium.)
hydrogenate to treat or cause to combine with hydrogen.
hydrogen bomb an extremely powerful bomb whose destructive energy comes from the fusion of hydrogen nuclei under intense heat and pressure, forming helium nuclei.
hydrogen ion the positive ion of a hydrogen atom whose electron has been removed, as in acids.
hydrogen peroxide an unstable compound of hydrogen and oxygen whose water solution is used mostly as an antiseptic or bleach.
hydrogen sulfide a poisonous, colorless gas that has the odor of rotten eggs and is used mostly in chemical manufacturing and metallurgy.
hydrography the study or science of describing or mapping the earth's bodies of water, esp. in relation to navigational or commercial uses.
hydroid characteristic of the asexual hydrozoan polyp. [2 definitions]
hydrologic pertaining to the circulation, distribution, or quality of the waters of the earth, or to the field of hydrology.
hydrological of or pertaining to the study of the earth's waters.
hydrology the scientific study of the distribution, circulation, and quality of the waters of the earth.
hydrolysis the decomposing of a chemical compound by combining it with water or the elements of water.
hydrolyte a substance that has gone through the process of hydrolysis.
hydrolyze to subject to or undergo hydrolysis.
hydrometer an instrument, usu. a sealed glass tube containing a graduated scale and weighted at one end, used to measure the specific gravity of liquids.
hydropathy the treatment of disease by the use of water, as by drinking or external application. (Cf. hydrotherapy.)
hydrophilic of or pertaining to a substance that has a strong affinity for water.
hydrophobia a deadly viral disease of the central nervous system, usu. transmitted by the bite of an infected animal; rabies. [2 definitions]
hydrophobic having a fear of water. [2 definitions]
hydrophyte a plant that grows in water alone or in esp. wet ground.