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hydrocarbon any of various organic compounds that contain only hydrogen and carbon, such as methane or ethylene.
hydrocephalus a condition, esp. in children, in which an abnormal amount of serum accumulates in the brain's ventricles, causing the skull to enlarge and the brain to compress.
hydrochloric acid a strong poisonous acid of hydrogen and chlorine in a water solution, esp. used for industrial and chemical purposes.
hydrochloride a salt formed by the combination of hydrochloric acid and an organic base.
hydrocortisone the hormone cortisol used pharmaceutically.
hydrocyanic acid a highly poisonous, flammable solution of hydrogen cyanide in water, used in manufacturing, working with metals, and the like; prussic acid.
hydrodynamics (used with a sing. verb) the science concerned with the motion of fluids, esp. as it relates to solid objects immersed in fluid, or with the motion of solid objects through fluids.
hydroelectric of or concerning the generation of electricity by means of the energy produced by moving water.
hydrofluoric acid a highly poisonous water solution of hydrogen fluoride, colorless and corrosive, used esp. in etching glass.
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.