/ Dictionary / Index S supposing: Meaning and Definition of Find definitions for: sup•pos•ing Pronunciation: (su-pō'zing), [key] — conj. upon the supposition or premise that; in the event that. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: supposing (Thesaurus) supposed supposition 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