noun
: any of a group of rare-earth metals separable as a group from other metals occurring with them and in addition to cerium including lanthanum, praseodymium, neodymium, promethium, samarium, and sometimes europium
noun
: any of a group of rare-earth metals separable as a group from other metals occurring with them and in addition to cerium including lanthanum, praseodymium, neodymium, promethium, samarium, and sometimes europium
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012