Source : Webster's Revised Unabridged Dictionary (1913)

Thulium \Thu"li*um\, n. [NL. See {Thule}.] (Chem.)
   A rare metallic element of uncertain properties and identity,
   said to have been found in the mineral gadolinite.

Source : WordNet®

thulium
     n : 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 [syn: {Tm}, {atomic number 69}]