noun🔗ShareActinidesAny of the 14 radioactive elements of the periodic table that are positioned under the lanthanides, to which they have similar chemistry."My chemistry textbook explains that the actinides are a series of radioactive elements, including uranium and plutonium, located below the lanthanides on the periodic table. "Mon manuel de chimie explique que les actinides sont une série d'éléments radioactifs, dont l'uranium et le plutonium, situés en dessous des lanthanides dans le tableau périodique.elementchemistryscienceChat with AIVocabulary GamePractice Reading