/ Dictionary / Index M MSS.: Meaning and Definition of Find definitions for: MSS. Pronunciation: [key] manuscripts. M.S.S. Pronunciation: [key] Master of Social Science. Master of Social Service. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. M.S.P.H.Ed. M.S.Sc. Related Content Daily Word Quiz: resilient Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language