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

These complex cylinders must hold deuterium and tritium fuel and withstand heat hotter than the Sun and pressure greater than a planet’s interior. —Aman Tripathi, Interesting Engineering, 27 Nov. 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

Oddly, that wouldn't be a problem if fusion plants were already abundant because there'd be so much surplus power that brute force methods could be used to produce tritium. —New Atlas, 2 Sep. 2025

Scientists have figured out how to collect helium-3 produced by the decay of tritium in nuclear weapons and power plants, but that yields less than 20 kg a year. —Jeremy Bogaisky, Forbes.com, 2 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