Antonyms of adj substantial

5 senses of substantial

Sense 1
significant, substantial -- (fairly large; "won by a substantial margin")

INDIRECT (VIA considerable) -> inconsiderable -- (too small or unimportant to merit attention; "passed his life in an inconsiderable village"; "their duties were inconsiderable"; "had no inconsiderable influence")

Sense 2
substantial, substantive -- (having a firm basis in reality and being therefore important, meaningful, or considerable; "substantial equivalents")

INDIRECT (VIA essential) -> inessential, unessential -- (not basic or fundamental)

Sense 3
substantial (vs. insubstantial), real, material -- (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)

insubstantial (vs. substantial), unsubstantial, unreal -- (lacking material form or substance; unreal; "as insubstantial as a dream"; "an insubstantial mirage on the horizon")
        => aeriform, aerial, airy, aery, ethereal -- (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")
        => shadowy, wraithlike -- (lacking in substance; "strange fancies of unreal and shadowy worlds"- W.A.Butler; "dim shadowy forms"; "a wraithlike column of smoke")
        => stringy -- (consisting of or containing string or strings)

Sense 4
hearty, satisfying, solid, square, substantial -- (providing abundant nourishment; "a hearty meal"; "good solid food"; "ate a substantial breakfast"; "four square meals a day")

INDIRECT (VIA wholesome) -> unwholesome -- (detrimental to physical or moral well-being; "unwholesome food"; "unwholesome habits like smoking")

Sense 5
solid, strong, substantial -- (of good quality and condition; solidly built; "a solid foundation"; "several substantial timber buildings")

INDIRECT (VIA sound) -> unsound -- (not in good condition; damaged or decayed; "an unsound foundation")

Similarity of adj substantial

5 senses of substantial

Sense 1
significant, substantial -- (fairly large; "won by a substantial margin")
       => considerable (vs. inconsiderable) -- (large or relatively large in number or amount or extent or degree; "a considerable quantity"; "the economy was a considerable issue in the campaign"; "went to considerable trouble for us"; "spent a considerable amount of time on the problem")

Sense 2
substantial, substantive -- (having a firm basis in reality and being therefore important, meaningful, or considerable; "substantial equivalents")
       => essential (vs. inessential) -- (basic and fundamental; "the essential feature")

Sense 3
substantial (vs. insubstantial), real, material -- (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)
          Also See-> material#2

Sense 4
hearty, satisfying, solid, square, substantial -- (providing abundant nourishment; "a hearty meal"; "good solid food"; "ate a substantial breakfast"; "four square meals a day")
       => wholesome (vs. unwholesome) -- (conducive to or characteristic of physical or moral well-being; "wholesome attitude"; "wholesome appearance"; "wholesome food")

Sense 5
solid, strong, substantial -- (of good quality and condition; solidly built; "a solid foundation"; "several substantial timber buildings")
       => sound (vs. unsound) -- (in good condition; free from defect or damage or decay; "a sound timber"; "the wall is sound"; "a sound foundation")