/ Dictionary / Index I insubstantial: Meaning and Definition of Find definitions for: in•sub•stan•tial Pronunciation: (in"sub-stan'shul), [key] — adj. not substantial or real; lacking substance: an insubstantial world of dreams. not solid or firm; weak; flimsy. not substantial in amount or size; inconsiderable: an insubstantial sum. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: insubstantial (Thesaurus) insubordinate insufferable Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language