/ Dictionary / Index R RdAc: Meaning and Definition of Find definitions for: RdAc Pronunciation: [key] — Symbol, Chem. radioactinium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. RDA RD&D; Related Content Daily Word Quiz: dissonant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language