Source : Webster's Revised Unabridged Dictionary (1913)

Polychrest \Pol"y*chrest\, n. [Gr. ? useful for many purposes;
   poly`s many + ? useful, fr. ? to use: cf. F. polychreste.]
   (Med.)
   A medicine that serves for many uses, or that cures many
   diseases. [Obs.]

   {Polychrest salt} (Old Med. Chem.), potassium sulphate,
      specifically obtained by fusing niter with sulphur.