/ Dictionary / Index S Sixtus III: Meaning and Definition of Find definitions for: Sixtus III Pronunciation: [key] popea.d.432–440. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Sixtus II Sixtus IV Related Content Daily Word Quiz: cetacean Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language