add. ·noun a metallic element of the rare earth group, found in gadolinite and some other minerals. symbol, er; at. wt. 167.4. its salts are rose-colored and give characteristic spectra.
2. erbium ·noun a rare metallic element associated with several other rare elements in the mineral gadolinite from ytterby in sweden. symbol er. atomic weight 165.9. its salts are rose-colored and give characteristic spectra. its sesquioxide is called erbia.