atomic number 18 atomic number 17 • atomic number 19 · · · Info · Definitions · Synonyms · Characters · · atomic number 18 · · Text Common · · Latin · · Scripts 16 · · Length 8 · · Syllables Definitions · · · (noun) a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere. Synonyms: argon, Ar, atomic number 18. · · Noun Definition 1 Synonyms · · · argon · · Synonym 1 ar · · Synonym 2 Characters · · space U+0020 1 digit one U+0031 8 digit eight U+0038 a latin small letter a U+0061 b latin small letter b U+0062 c latin small letter c U+0063 e latin small letter e U+0065 i latin small letter i U+0069 m latin small letter m U+006D n latin small letter n U+006E o latin small letter o U+006F r latin small letter r U+0072 t latin small letter t U+0074 u latin small letter u U+0075