/ Dictionary / Index S subst.: Meaning and Definition of Find definitions for: subst. Pronunciation: [key] substantive. substantively. substitute. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. subspecific substage Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language