WordNet sense 1 (resembling air or having the form of air):

airlike

WordNet sense 2 (existing as or having characteristics of a gas):

gaseous

WordNet sense 3 (characterized by lightness and insubstantiality; as impalpable or intangible as air):

aerial, airy, ethereal, aery, aerial

WordNet sense 4 (lacking material form or substance; unreal):

insubstantial, unreal, unsubstantial