trit·i·um (trĭtē-əm, trĭshē-)
A rare radioactive isotope of hydrogen, H-3, having one proton and two neutrons in the nucleus and a half-life of 12.3 years, prepared artificially for use as a tracer and as a constituent of hydrogen bombs.
[From Greek tritos, third; see trei- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.