/ Dictionary / Index S supposition: Meaning and Definition of Find definitions for: sup•po•si•tion Pronunciation: (sup"u-zish'un), [key] — n. the act of supposing. something that is supposed; assumption; hypothesis. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: supposition (Thesaurus) supposing suppositious Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language