Definitions for "Didymium"
A rare metallic substance usually associated with the metal cerium; -- hence its name. It was formerly supposed to be an element, but has since been found to consist of two simpler elementary substances, neodymium and praseodymium. See Neodymium, and Praseodymium.
a mixture of praseodymium (Pr) and neodymium (Nd) believed to be an element until 1885. [Mendeleev, Newlands
The combination of two rare earth elements: neodymium and praseodymium. Glass filter lenses made of didymium doped glass absorb infrared and ultraviolet radiation, and the yellow flare produced by hot glass.