1. A soft silvery metallic element of the rare earth group; isotope 170 emits X-rays and is used in small portable X-ray machines; it occurs in monazite and apatite and xenotime
   - thulium, atomic number 69

Type of: metal, metallic element

Part of: apatite, monazite, xenotime

Encyclopedia: Tm

• umiak
• umlaut
• Umma
• Umma Tameer-e-Nau
• Ummah
• ump
• umpirage
• umpire
• umpteen
• umpteenth
• umptieth
• umteen
• umteenth
• UN agency
• un-
• un-American
• un-come-at-able
• una corda
• unabashed
• unabashedly
• unabated
• unable
• unable to help
• unabridged
• unabridged dictionary