insubstantial

insubstantial adjective airy, baseless, bodiless, chimerical, ephemeral, fanciful, feeble, flimsy, fragile, frail, groundless, hallucinatory, illusive, illusory, imaginary, imagined, immaterial, impalpable, inadequate, inconsiderable, incorporeal, infirm, insignificant, lacking firmness, lacking substance, lame, made poorly, modest, nonexistent, notional, of no consequence, petty, picayune, poor, powerless, scant, slender, slight, slim, spectral, superficial, tenuous, thin, trifling, unbased, unfirm, unfounded, ungrounded, unreal, unsolid, unsound, unsubstantial, unsustainable, untenable, vague, visionary, weak, without basis, without foundation, without plausibility, without reality, wobbly, worthless

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See also: circumstantial, collateral, deficient, delusive, fallacious, illusory, immaterial, inadequate, inappreciable, inconsiderable, insignificant, insipid, intangible, invalid, minor, negligible, nonsubstantial, nugatory, null, perfunctory, remote, superficial, unfounded, unsound, void