/ Dictionary / Index R R horizon: Meaning and Definition of Find definitions for: R horizon Pronunciation: [key] bedrock immediately underlying layers of soil. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. rhopalid bug rhotacism Related Content Daily Word Quiz: clairvoyant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language