RU-486 \ˈärˌyüˌfōrˌād.ēˈsiks, -ˌfȯr-\noun Etymology:Roussel-UCLAnglo-French, the drug's French manufacturer + 486, laboratory serial number : a drug C29H35NO2 taken orally to induce abortion especially early in pregnancy by blocking the body's use of progesterone — called also mifepristone