n. [ NL. See Gadolinite. ] (Chem.) A rare earth metallic element of the Lanthanide series, with a characteristic spectrum, found associated with yttrium and other rare earth elements. Symbol, Gd; it has an atomic number of 64, an atomic weight of 157.25 (C=12.011), and a valence of +3. [ 1913 Webster +PJC ]