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

From the early 1950s until the end of the Cold War, its primary mission was producing plutonium and tritium for the US nuclear weapons arsenal. —Aman Tripathi, Interesting Engineering, 3 Oct. 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

These neutrons interact with the lithium to eventually produce tritium. —New Atlas, 2 Sep. 2025

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

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