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]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "aureole":
   O, annular muscle, annulus, anthelion, antisun, areola, aura,
   chaplet, circle, circuit, circumference, circus, closed circle,
   corona, coronet, countersun, crown, cycle, diadem, discus, disk,
   eternal return, fairy ring, garland, glory, halo, lasso,
   logical circle, loop, looplet, lunar corona, lunar halo,
   magic circle, mock moon, mock sun, moon dog, nimbus, noose, orbit,
   paraselene, parhelic circle, parhelion, radius, rainbow, ring,
   rondelle, round, roundel, saucer, solar corona, solar halo,
   sphincter, sun dog, vicious circle, wheel, wreath