The Collaborative International Dictionary of English v.0.48:

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.
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         Go, soar with Plato to the empyreal sphere. --Pope.
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   Empyreal air, oxygen gas.
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