Definition of "unsubstantial"

unsubstantial

adjective
comparative more unsubstantial, superlative most unsubstantial
1. (archaic) Insubstantial.
  Quotations
  What boots it, that my Fortune decks me thus / With unſubſtantial Plumes; when my Heart groans / Beneath the gay Capariſon, and Love / With unrequited Paſſion wounds my Soul!
  1749, [Tobias George Smollett], The Regicide: Or, James the First, of Scotland. A Tragedy. […], London: […] [F]or the benefit of the author, Act III, scene iv, page 37
  They are (said he) meer phantoms of ignorance and credulity, swelled up in the repetition, like those unsubstantial bubbles which the boys blow up in sopasuds with a tobacco pipe.
  1751, [Tobias] Smollett, chapter 89, in The Adventures of Peregrine Pickle […], volume III, London: Harrison and Co., […]
  They shook hands upon it, and Sydney turned away. Within a minute afterward he was, to all outward appearance, as unsubstantial as ever.
  1859, Charles Dickens, A Tale of Two Cities, London: Chapman and Hall, […]