/ Dictionary / Index U unsubstantial: Meaning and Definition of Find definitions for: un•sub•stan•tial Pronunciation: (un"sub-stan'shul), [key] — adj. not substantial; having no foundation in fact; fanciful; insubstantial: an unsubstantial argument; unsubstantial hopes. without material substance: an unsubstantial ghost. lacking material substance; materially paltry: an unsubstantial dinner of bread and cheese. lacking strength or solidity; flimsy: an unsubstantial wall of cardboard. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: unsubstantial (Thesaurus) unstudied unsubstantiated Related Content Daily Word Quiz: fabricate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language