terbium terbium /ˈtɜːrbiəm/

noun

1. A metallic element of the rare earth group; used in lasers; occurs in apatite and monazite and xenotime and ytterbite  ( atomic number 65 , Tb , terbium )
   a metallic element of the rare earth group; used in lasers; occurs in apatite and monazite and xenotime and ytterbite