ˈi.trēəm noun
( -s )
Etymology: New Latin, from yttria, after such pairs as New Latin lithia : lithium
: a trivalent metallic element that is usually included among the rare-earth metals because it resembles them chemically and occurs with them in several minerals (as gadolinite, xenotime, yttrotantalite, euxenite) — symbol Y ; see element table