Definitions for "Deuterium"
a heavy isotope of hyrogen containing on proton and one neutron
Deuterium is the isotope of hydrogen with one proton and one neutron, D = 2H. On average, one out of every 6700 hydrogen atoms found in nature is deuterium. Processes are well developed for separating water molecules containing deuterium atoms, or "heavy water," so that the deuterium fuel for fusion reactions is essentially free. For more information on hydrogen and its isotopes see the Los Alamos periodic table
The isotope of hydrogen that has one neutron.