·noun A rare earth, regarded by some as an oxide of the supposed element gadolinium, by others as only a mixture of the oxides of yttrium, erbium, ytterbium, ·etc.
II. Gadolinia ·add. ·noun A rare earth associated with yttria and regarded as the oxide (Gd2O3) of a metallic element, Gad``o*lin"i*um (/), with an assigned atomic weight of 153.3.