/ Dictionary / Index R rms: Meaning and Definition of Find definitions for: rms Pronunciation: [key] (often cap.) See R.M.S. Pronunciation: [key] Railway Mail Service. Royal Mail Service. Royal Mail Steamship. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. rmdr Rn Related Content Daily Word Quiz: philtrum Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language