\Yt"tri*um\, n. [NL., from Ytterby, in Sweden. See
{Erbium}.] (Chem.)
A rare metallic element of the boron-aluminium group, found
in gadolinite and other rare minerals, and extracted as a
dark gray powder. Symbol Y. Atomic weight, 89. [Written also
{ittrium}.]
Note: Associated with yttrium are certain rare elements, as
      erbium, ytterbium, samarium, etc., which are separated
      in a pure state with great difficulty. They are studied
      by means of their spark or phosphorescent spectra.
      Yttrium is now regarded as probably not a simple
      element, but as a mixture of several substances.