noun.
A soft, bright, silvery rare-earth element occurring in three allotropic forms and used as an x-ray source for portable irradiation devices, as a dopant for laser materials, and in solar cells and some special alloys. Atomic number 70; atomic weight 173.05; melting point 824°C; boiling point 1,196°C; specific gravity 6.903 (alpha form), 6.966 (beta form); valence 2, 3. cross-reference: Periodic Table.