argon: a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere
noble gas: any of the chemically inert gaseous elements of the helium group in the periodic table
nuclear winter: a long period of darkness and extreme cold that scientists predict would follow a full-scale nuclear war; a layer of dust and smoke in the atmosphere would cover the earth and block the rays of the sun; most living organisms would perish