heavy water

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heav·y wa·ter

D2O; water in which the hydrogen atoms are deuterium, or heavy hydrogen (2H), with physical properties that differ noticeably from those of ordinary water; an elevated presence will cause a decrease in metabolic activity; used as a moderator in nuclear reactors because of its capacity to absorb neutrons.
Synonym(s): deuterium oxide

heavy water

water in which the hydrogen component is deuterium (2H), or heavy hydrogen. It has properties different from those of ordinary water. Because of its ability to absorb neutrons, heavy water is used as a moderator in nuclear reactions. Also written as D2O.

heavy water

D2O; an isotopic variety of water, esp. deuterium oxide, in which hydrogen has been displaced by its isotope, deuterium. Its properties differ from ordinary water in that heavy water has a higher freezing and boiling point and does not support life.
See also: water