tritium

noun

tri·​ti·​um ˈtri-tē-əm  ˈtri-shē- 

: a radioactive isotope of hydrogen that has one proton and two neutrons in its nucleus and that has three times the mass of ordinary hydrogen

—symbol T

Examples of tritium in a Sentence

Recent Examples on the Web

Helium-3 production depends on aging tritium stockpiles, which is a source that is both strictly limited and prohibitively expensive to expand. — Mrigakshi Dixit, Interesting Engineering, 21 July 2026

There are also slots for glow-in-dark tritium tubes, but the tubes themselves are sold separately. — Maryna Holovnova, New Atlas, 15 July 2026

This wastewater can contain small amounts of radioactive tritium, and the current ALARA objective is to keep the radiation exposure from this wastewater to 3 mrem per year or less. — Stephanie Pappas, Scientific American, 10 July 2026

Word History

Etymology

New Latin, from Greek tritos third — more at third entry 1

First Known Use

1933, in the meaning defined above

Kids Definition

tritium

noun

tri·​ti·​um ˈtrit-ē-əm  ˈtrish-ē- 

: a rare radioactive form of hydrogen having atoms with three times the mass of ordinary light hydrogen atoms

Medical Definition

tritium

noun

tri·​ti·​um ˈtrit-ē-əm  ˈtrish-ē- 

: a radioactive isotope of hydrogen that has three times the mass of ordinary hydrogen

—symbol T