Source : Webster's Revised Unabridged Dictionary (1913)

Empyreal \Em*pyr"e*al\, a. [L. empyrius, empyreus, fiery, Gr. ?,
   ?, in fire, fiery; ? in + ? fire. See {In}, and {Fire}.]
   Formed of pure fire or light; refined beyond a["e]rial
   substance; pertaining to the highest and purest region of
   heaven.

         Go, soar with Plato to the empyreal sphere. --Pope.

   {Empyreal air}, oxygen gas.