Terbium \Ter"bi*um\, n. [NL., fr. Ytterby, in Sweden. See Erbium.]

(Chem.) A rare metallic element, of uncertain identification, supposed to exist in certain minerals, as gadolinite and samarskite, with other rare ytterbium earth. Symbol Tr or Tb. Atomic weight 150.

Source: Webster's Revised Unabridged Dictionary (1913)