Source : Webster's Revised Unabridged Dictionary (1913)

Lavoesium \La*v[oe]"si*um\, n. [NL., fr. Lavoisier, the
   celebrated French chemist.] (Chem.)
   A supposed new metallic element. It is said to have been
   discovered in pyrites, and some other minerals, and to be of
   a silver-white color, and malleable.