The term 'smeltery waste' refers to the byproducts of metal smelting, which is the process of extracting metals from ore. The two crossword solutions for this term are 'SLAG' and 'DROSS, ' both of which are solid waste materials that are created during the smelting process. SLAG is a glassy, granular material that is formed when impurities are removed from the molten metal, while DROSS is a mixture of metal oxides and other impurities that float to the surface of the molten metal.