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

Most experts agree that significant technical hurdles in plasma confinement, tritium fuel cycle management, and first-wall materials must be overcome before commercial fusion becomes reality. —Dave Smith, Fortune, 18 Dec. 2025

This work represents the most sensitive search to date for sterile neutrinos using tritium beta decay. —Mrigakshi Dixit, Interesting Engineering, 3 Dec. 2025

There are direct tritium beta decay experiments (like KATRIN) that are ongoing, seeking to measure the individual neutrino mass eigenstates (ν1, ν2, and ν3) directly. —Big Think, 28 Oct. 2025

Pentagon estimates from last year said China was on track to have more than 1,000 operational nuclear warheads by 2030, although Western analysts say Beijing's stockpile will depend on how much plutonium, highly enriched uranium and tritium China can access. —Ellie Cook — Reporting From Prague, Czech Republic, MSNBC Newsweek, 3 Sep. 2025

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