n. Symbol Mt An artificially produced radioactive element with atomic number 109 that has known isotopes with mass numbers ranging from 265 to 279. The isotope with the longest confirmed half-life (0.7 seconds) is Mt-268. See Periodic Table. [After Lise Meitner.] |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.