/ Dictionary / Index U unsubstantiated: Meaning and Definition of Find definitions for: un•sub•stan•ti•at•ed Pronunciation: (un"sub-stan'shē-ā"tid), [key] — adj. not substantiated; unproved or unverified: unsubstantiated allegations. being without form or substance. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: unsubstantiated (Thesaurus) unsubstantial unsuccess 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