/ Dictionary / Index S suppositious: Meaning and Definition of Find definitions for: sup•po•si•tious Pronunciation: (sup"u-zish'us), [key] — adj. formed from or growing out of supposition: suppositious evidence. supposititious. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: suppositious (Thesaurus) supposition supposititious Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language