any of a subgroup of rare-earth metals, of which the cerium and yttrium metals comprise the other two subgroups.
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British Dictionary definitions for terbium metal
chem any of a group of related lanthanides, including terbium, europium, and gadolinium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012