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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"
(often followed by `to') lacking importance; not mattering one way or the other; "whether you choose to do it or not is a matter that is quite immaterial (or indifferent)"; "what others think is altogether indifferent to him"
having substance or capable of being treated as fact; not imaginary; "the substantial world"; "a mere dream, neither substantial nor practical"; "most ponderous and substantial things"- Shakespeare