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

Low levels of tritium were found in ground water last year, and the latest monitoring showed that concentrations have declined along the western side of Unit 2. —Teri Sforza, Oc Register, 11 June 2025

Other features include a tungsten-steel automotive window glass breaker, a keyring/lanyard hole, and two slots for adding optional vials of glow-in-the-dark tritium. —Ben Coxworth may 27, New Atlas, 27 May 2025

But Berzin said that the design will incorporate a layer of lithium that will form tritium when bombarded by neutrons from the stellarator. —ArsTechnica, 1 Apr. 2025

So, engineers will need to develop the ability to produce tritium within the fusion device itself. —Farhat Beg, The Conversation, 8 Jan. 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