Source : Webster's Revised Unabridged Dictionary (1913)

Ethereal \E*the"re*al\, a.
   1. Pertaining to the hypothetical upper, purer air, or to the
      higher regions beyond the earth or beyond the atmosphere;
      celestial; as, ethereal space; ethereal regions.

            Go, heavenly guest, ethereal messenger. --Milton.

   2. Consisting of ether; hence, exceedingly light or airy;
      tenuous; spiritlike; characterized by extreme delicacy, as
      form, manner, thought, etc.

            Vast chain of being, which from God began, Natures
            ethereal, human, angel, man.          --Pope.

   3. (Chem.) Pertaining to, derived from, or resembling, ether;
      as, ethereal salts.

   {Ethereal oil}. (Chem.) See {Essential oil}, under
      {Essential}.

   {Ethereal oil of wine} (Chem.), a heavy, yellow, oily liquid
      consisting essentially of etherin, etherol, and ethyl
      sulphate. It is the oily residuum left after
      etherification. Called also {heavy oil of wine}
      (distinguished from oil of wine, or [oe]nanthic ether).

   {Ethereal salt} (Chem.), a salt of some organic radical as a
      base; an ester.

Source : WordNet®

ethereal
     adj 1: characterized by lightness and insubstantiality; as
            impalpable or intangible as air; "figures light and
            aeriform come unlooked for and melt away"- Thomas
            Carlyle; "aerial fancies"; "an airy apparition";
            "physical rather than ethereal forms" [syn: {aeriform},
             {aerial}, {airy}, {aery}]
     2: of or containing or dissolved in ether; "ethereal solution"
     3: of heaven or the spirit; "celestial peace"; "ethereal
        melodies"; "the supernal happiness of a quiet death" [syn:
         {celestial}, {supernal}]
     4: characterized by unusual lightness and delicacy; "this
        smallest and most ethereal of birds"; "gossamer shading
        through his playing" [syn: {gossamer}]