Any of the chemically inert gaseous elements of the helium group in the periodic table WordNet 3.0 & Open English WordNet

The noble gases are the naturally occurring members of group 18 of the periodic table: helium, neon, argon, krypton, xenon, and radon. Wikipedia

Historically called inert gas Wikipedia Disambiguation

Group of chemical elements in column 18 of the priodic table, that tend to be chemically inert and thus form odorless, colorless, monatomic gases with low reactivity; consists of helium, neon, argon, krypton, xenon, radon, and possibly oganesson Wikidata

Any one of the monatomic gaseous elements forming group 18 (formerly group 0) of the periodic table. OmegaWiki

Any of the elements of group 18 of the periodic table, being monatomic and (with very limited exceptions) inert. Wiktionary

Element of group 18 of the periodic table. Wiktionary (translation)