noun Chemistry.

  1. an isotope of hydrogen, having twice the mass of ordinary hydrogen; heavy hydrogen. Symbol: D; atomic weight: 2.01; atomic number: 1.


  1. a stable isotope of hydrogen, occurring in natural hydrogen (156 parts per million) and in heavy water: used as a tracer in chemistry and biology. Symbol: D or ²H; atomic no: 1; atomic wt: 2.014; boiling pt: –249.7°C

1933, coined by U.S. chemist Harold C. Urey, with Modern Latin ending + Greek deuterion, neuter of deuterios “having second place,” from deuteros “second,” from duo (see two). So called because it is twice the mass of hydrogen.


  1. An isotope of hydrogen with one proton and one neutron in the nucleus having an atomic weight of 2.014.heavy hydrogen hydrogen-2

  1. An isotope of hydrogen whose nucleus has one proton and one neutron and whose atomic mass is 2. Deuterium is used widely as a tracer for analyzing chemical reactions, and it combines with oxygen to form heavy water. Also called heavy hydrogen See Note at heavy water.
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