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[thoo-lee-uh m] /ˈθu li əm/
noun, Chemistry.
a rare-earth metallic element found in the minerals euxenite, gadolinite, etc. Symbol: Tm; atomic weight: 168.934; atomic number: 69; specific gravity: 9.32.
Origin of thulium
1875-80; < New Latin; see Thule, -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for thulium


a malleable ductile silvery-grey element occurring principally in monazite. The radioisotope thulium-170 is used as an electron source in portable X-ray units. Symbol: Tm; atomic no: 69; atomic wt: 168.93421; valency: 3; relative density: 9.321; melting pt: 1545°C; boiling pt: 1950°C
Word Origin
C19: New Latin, from Thule + -ium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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thulium in Medicine

thulium thu·li·um (thōō'lē-əm, thyōō'-)
Symbol Tm
A rare-earth element having an x-ray emitting isotope that is used in small portable medical x-ray units. Atomic number 69; atomic weight 168.934; melting point 1,545°C; boiling point 1,946°C; specific gravity 9.3; valence 3.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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thulium in Science
Symbol Tm
A soft, silver-gray metallic element of the lanthanide series. One of its artificial radioactive isotopes is used as a radiation source in small, portable x-ray machines. Atomic number 69; atomic weight 168.934; melting point 1,545°C; boiling point 1,727°C; specific gravity 9.3; valence 2, 3. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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