Source : Webster's Revised Unabridged Dictionary (1913)

Terbium \Ter"bi*um\, n. [NL., fr. Ytterby, in Sweden. See
   {Erbium}.] (Chem.)
   A rare metallic element, of uncertain identification,
   supposed to exist in certain minerals, as gadolinite and
   samarskite, with other rare ytterbium earth. Symbol Tr or Tb.
   Atomic weight 150.

Source : WordNet®

terbium
     n : a metallic element of the rare earth group; used in lasers;
         occurs in apatite and monazite and xenotime and ytterbite
         [syn: {Tb}, {atomic number 65}]