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 is used in portable X-ray devices for medical and dental diagnostics";
   - Tm, atomic number 69

Derived forms: thuliums

Type of: metal, metallic element

Part of: apatite, monazite, xenotime

Encyclopedia: Thulium