promethium: a soft silvery metallic element of the rare earth group having no stable isotope; was discovered in radioactive form as a fission product of uranium
metallic element: any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
conservative judaism: Jews who keep some of the requirements of the Mosaic law but allow for adaptation of other requirements (as some of the dietary laws) to fit modern circumstances