The Collaborative International Dictionary of English v.0.48:

Europium \Eu*ro"pi*um\, n. [NL.; Europe + -ium, as in
   aluminium.] (Chem.)
   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. +PJC]

WordNet (r) 3.0 (2006):

europium
    n 1: a bivalent and trivalent metallic element of the rare earth
         group [syn: europium, Eu, atomic number 63]

The Elements (07Nov00):

europium
Symbol: Eu
Atomic number: 63
Atomic weight: 151.25
Soft silvery metallic element belonging to the lanthanoids. Eu-151 and
Eu-153 are the only two stable isotopes, both of which are neutron
absorbers. Discovered in 1889 by Sir William Crookes.