thulium Meaning, Definition & Usage

  1. noun 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
    Tm; atomic number 69.

WordNet

Thu"li*um noun
Etymology
NL. See Thule.
Definitions
  1. (Chem.) A rare metallic element of uncertain properties and identity, said to have been found in the mineral gadolinite.

Webster 1913