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

The Savannah River Site was built in 1951 as a means to produce material for nuclear weapons, primarily tritium and plutonium, to support America’s defense programs, according to the SRS website. —Angel Saunders, People.com, 31 July 2025

The fuel sources—tritium and deuterium—come from easily accessible sources, namely seawater and lithium, and should be cheap to produce compared to fossil fuels. —Justin Worland, Time, 17 July 2025

Fuel for fusion is abundant, derived from a form of hydrogen found in seawater and tritium extracted from lithium. —Ella Nilsen, CNN Money, 30 June 2025

The move was backed by the International Atomic Energy Agency and the plant operator TEPCO says all radioactive elements have been filtered out except for tritium, levels of which are within safe limits. —Afp, Fortune, 30 June 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