/ Dictionary / Index S supposititious: Meaning and Definition of Find definitions for: sup•pos•i•ti•tious Pronunciation: (su-poz"i-tish'us), [key] — adj. fraudulently substituted or pretended; spurious; not genuine. hypothetical. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: supposititious (Thesaurus) suppositious suppositive 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