(1):
(n.) 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.
(2):
(n.) 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.