The term 'soft silvery-white metallic element' can be described by two crossword solutions: POTASSIUM (9 letters) and Indium (6 letters). POTASSIUM is a chemical element with the symbol K and atomic number 19. It is a soft, silvery-white alkali metal that is highly reactive and flammable. Indium is a chemical element with the symbol In and atomic number 49. It is a soft, silvery-white metal that is malleable and ductile. Both elements are found in nature and have many uses in industry.