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The Collaborative International Dictionary of English v.0.48 (gcide)

Yttrium \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 number 39. Atomic weight,
88.9. [Written also {ittrium}.]
[1913 Webster PJC]

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.
[1913 Webster]