'tritium' definitions:

Definition of 'tritium'

From: WordNet
noun
A radioactive isotope of hydrogen; atoms of tritium have three times the mass of ordinary hydrogen atoms

Definition of 'tritium'

From: GCIDE
  • tritium \trit"i*um\ (tr[i^]t"[i^]*[u^]m), n. (Chem.) A radioactive isotope of hydrogen having one proton and two neutrons in the nucleus. It decays spontaneously to Helium-3 by the emission of an electron (beta ray), with a half-life of 12.3 years. Symbol 1H3. Atomic weight 3.01605 (C-12 = 12.0000). It is one of the radioisotopes commonly used to label chemical compounds for use as tracers in biochemistry and chemistry. It is also used as one of the fusionable components of a hydrogen bomb. [PJC]