/ Dictionary / Index O O.S.A.: Meaning and Definition of Find definitions for: O.S.A. Pronunciation: [key] Order of St. Augustine (Augustinian). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. os Osage Related Content Daily Word Quiz: deleterious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language