- erbium, Er, atomic number 68 - a trivalent metallic element of the rare earth group; occurs with yttrium
--1 is a kind of metallic element, metal
--1 is a substance of gadolinite, ytterbite; fergusonite - emergency room, ER - a room in a hospital or clinic staffed and equipped to provide emergency care to persons requiring immediate medical treatment
--2 is a kind of hospital room