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[yoo-ni-len-ee-uh m] /ˌyu nɪˈlɛn i əm/
noun, Chemistry, Physics.
former name of meitnerium. Symbol: Une.
Also called element 109.


[mahyt-nur-ee-uh m] /maɪtˈnɜr i əm/
noun, Chemistry, Physics.
a superheavy, synthetic, radioactive element. Symbol: Mt; atomic number: 109.
Formerly unnilennium, element 109.
Origin of meitnerium
named after Austrian physicist Lise Meitner; see -ium

element 109

noun, Chemistry, Physics.
Formerly unnilennium. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2016.
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British Dictionary definitions for unnilennium


a synthetic element produced in small quantities by high-energy ion bombardment. Symbol: Mt; atomic no: 109
Word Origin
C20: named after Lise Meitner
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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unnilennium in Science
Symbol Mt
A synthetic, radioactive element that is produced by bombarding bismuth with iron ions. Its most long-lived isotopes have mass numbers of 266 and 268 with half-lives of 3.4 milliseconds and 70 milliseconds, respectively. Atomic number 109. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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