n. [ NL., fr. Ytterby, in Sweden. See Erbium. ] (Chem.) A rare metallic element, found in certain minerals, as gadolinite and samarskite, with other rare earths such as ytterbium. Symbol Tb. Atomic number 65. Atomic weight 158.925. [ 1913 Webster +PJC ]
n. [ NL., fr. Ytterby, in Sweden. See Erbium. ] (Chem.) A rare element of the boron group, sometimes associated with yttrium or other related elements, as in euxenite and gadolinite. Symbol Yb; provisional atomic weight 173.2. Cf. Yttrium. [ 1913 Webster ]
☞ Ytterbium is associated with other rare elements, and probably has not been prepared in a pure state. [ 1913 Webster ]