aeriform
/ˈɛːrɪfɔːm/adjective
1Of the form or nature of a gas; gaseous. Now chiefly historical.
2 Figurative. Insubstantial, intangible, unreal.
Origin
Late 18th century; earliest use found in Richard Kirwan (1733–1812), chemist and mineralogist. From classical Latin āēr air + -iform, after French aériforme. Compare Italian aeriforme.