Definitions for noble gas
Random House Webster's College Dictionary
any of the chemically inert gaseous elements of group 8A or 0 of the periodic table: helium, neon, argon, krypton, xenon, and radon.
Ref: Also called inert gas.
Origin of noble gas:
noble gas, inert gas, argonon(noun)
any of the chemically inert gaseous elements of the helium group in the periodic table
Any of the elements of group 18 of the periodic table, being monatomic and (with very limited exceptions) inert.