émaniumcommon nounSyllable DecompositionémaniumEtymologyexpandemanating, because the element transforms into radon, a radioactive gas. Friedrich Oskar Giesel initially called it emanationskörper, 'emanating substance'.Definition1. Name given by the German chemist Friedrich Oskar (Fritz) Giesel to a radioactive chemical element, accompanying lanthanum and cerium in pitchblende ores, and distinguished by its production of a radioactive gaseous emanation. It was later found to be actinium.flags.désuetchimieexpandSynonymactinium