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

Blanket Test Facility Engineers would use the facility to confirm that circulating blanket fluids can effectively remove heat, withstand mechanical stress, and safely extract fuel at power plant levels—critical steps needed before advancing to more complex neutron and tritium testing. —Prabhat Ranjan Mishra, Interesting Engineering, 13 June 2026

The product also includes optional tritium tube inserts for better visibility in the dark. —Maryna Holovnova, New Atlas, 25 May 2026

On terra firma, most of the available supply of helium-3 comes as a by-product of nuclear weaponry via the radioactive decay of tritium, a rare isotope of hydrogen that boosts the power of thermonuclear bombs. —Robin George Andrews, Scientific American, 14 May 2026

It’s derived from deuterium, found in seawater, and tritium, which is extracted from lithium. —Ella Nilsen, CNN Money, 30 Apr. 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