rhenium: a rare heavy polyvalent metallic element that resembles manganese chemically and is used in some alloys; is obtained as a by-product in refining molybdenum
metallic element: any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
existentialism: (philosophy) a 20th-century philosophical movement chiefly in Europe; assumes that people are entirely free and thus responsible for what they make of themselves