/ Dictionary / Index R RU 486: Meaning and Definition of Find definitions for: RU 486 Pronunciation: [key] an antigestational drug, in the form of a pill, that prevents a fertilized egg from attaching to the uterine wall by blocking the action of progesterone. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Ru ruana Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language