Real Dictionary

argon
uncountable noun: Argon is an inert gas which exists in very small amounts in the atmosphere. It is used in electric lights.

argon in American English
a colorless, odorless chemical element, one of the noble gases, constituting nearly 1% of the atmosphere: it is used in incandescent light bulbs, radio tubes, welding, etc.: symbol, Ar; at. no., 18
noun: a colorless, odorless, chemically inactive, monatomic, gaseous element that, because of its inertness, is used for filling fluorescent and incandescent lamps and vacuum tubes; at. no.: 18; at. wt.: 39.948

argon in British English
noun: an extremely unreactive colourless odourless element of the rare gas series that forms almost 1 per cent (by volume) of the atmosphere. It is used in electric lights. Symbol: Ar; atomic no: 18; atomic wt: 39.948; density: 1.7837 kg/m3; freezing pt: –189.3