Source : Webster's Revised Unabridged Dictionary (1913)

Aeriform \A"["e]r*i*form\ (?; 277), a. [L. a["e]r air + -form:
   cf. F. a['e]riforme.]
   Having the form or nature of air, or of an elastic fluid;
   gaseous. Hence fig.: Unreal.

Source : WordNet®

aeriform
     adj 1: resembling air or having the form of air [syn: {airlike}]
     2: characterized by lightness and insubstantiality; as
        impalpable or intangible as air; "figures light and
        aeriform come unlooked for and melt away"- Thomas Carlyle;
        "aerial fancies"; "an airy apparition"; "physical rather
        than ethereal forms" [syn: {aerial}, {airy}, {aery}, {ethereal}]