noun an elementary substance which forms one of the constituents of didymium. symbol nd. atomic weight 140.8.
2. neodymium ·add. ·noun a rare metallic element occurring in combination with cerium, lanthanum, and other rare metals, and forming amethyst-colored salts. it was separated in 1885 by von welsbach from praseodymium, the two having previously been regarded as a single element (didymium). it is chiefly trivalent. symbol nd; at. wt. 144.3.