/ Dictionary / Index R R.R.R.: Meaning and Definition of Find definitions for: R.R.R. Pronunciation: [key] return receipt requested (used in registered mail). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. rRNA RRT Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language