gadolinium: a ductile silvery-white ductile ferromagnetic trivalent metallic element of the rare earth group
metallic element: any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
phenylketonuria: a genetic disorder of metabolism; lack of the enzyme needed to turn phenylalanine into tyrosine results in an accumulation of phenylalanine in the body fluids which causes various degrees of mental deficiency