Meaning of rare-earth element

rare'-earth' el"ement

Pronunciation: (râr'ûrth'), [key]
— Chem. Chem.
  1. any of a group of closely related metallic elements, comprising the lanthanides, scandium, and yttrium, that are chemically similar by virtue of having the same number of valence electrons. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.