europium(n = noun.substance) atomic number 63, eu - a bivalent and trivalent metallic element of the rare earth group;
is a kind of metal, metallic element

   A metallic element of the rare-earth group (Lanthanide series), discovered spectroscopically by Demarcay in 1896. Symbol, Eu; atomic number 63; at. wt., 151.965 (C=12.011); valence = +2 or +3. [Webster 1913 Suppl.]

europium, n. Chem. a soft silvery metallic element of the lanthanide series, occurring naturally in small quantities.

Usage:
Symb.: Eu.

Etymology:
mod.L f. Europe