The Collaborative International Dictionary of English v.0.48:

Aureola \Au*re"o*la\, Aureole \Au"re*ole\, n. [F. aur['e]ole,
   fr. L. aureola, (fem adj.) of gold (sc. corona crown), dim.
   of aureus. See Aureate, Oriole.]
   1. (R. C. Theol.) A celestial crown or accidental glory added
      to the bliss of heaven, as a reward to those (as virgins,
      martyrs, preachers, etc.) who have overcome the world, the
      flesh, and the devil.
      [1913 Webster]

   2. The circle of rays, or halo of light, with which painters
      surround the figure and represent the glory of Christ,
      saints, and others held in special reverence.
      [1913 Webster]

   Note: Limited to the head, it is strictly termed a nimbus;
         when it envelops the whole body, an aureola.
         --Fairholt.
         [1913 Webster]

   3. A halo, actual or figurative.
      [1913 Webster]

            The glorious aureole of light seen around the sun
            during total eclipses.                --Proctor.
      [1913 Webster]

            The aureole of young womanhood.       --O. W.
                                                  Holmes.
      [1913 Webster]

   4. (Anat.) See Areola, 2.
      [1913 Webster]

   5. the outermost region of the sun's atmosphere; visible from
      earth during a solar eclipse, or in outer space by the use
      of special instruments; a corona[5].

   Syn: corona.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

aureole
    n 1: the outermost region of the sun's atmosphere; visible as a
         white halo during a solar eclipse [syn: aureole,
         corona]
    2: an indication of radiant light drawn around the head of a
       saint [syn: aura, aureole, halo, nimbus, glory,
       gloriole]