Synonyms for Insubstantial (same or very similar meaning)
WordNet sense 1 (lacking in nutritive value):
jejune
WordNet sense 2 (detrimental to physical or moral well-being):
unwholesome
WordNet sense 3 (characterized by lightness and insubstantiality; as impalpable or intangible as air):
aerial, airy, aerial
WordNet sense 4 (lacking material form or substance; unreal):
unreal, unsubstantial
From the ODE community, based on WordNet
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