The Collaborative International Dictionary of English v.0.48:

aeon \aeon\, AEon \[AE]"on\, n.
   1. A period of immeasurable duration. See Eon.
      [1913 Webster]

   2. (Gnosticism) a divine power or nature emanating from the
      Supreme Being and playing various roles in the operation
      of the universe.

   Syn: eon
        [WordNet 1.5]

   3. the longest division of geological time; two or more eras.

   Syn: eon
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Eon \E"on\, aeon \[ae]"on\, n. [L. aeon, fr. Gr. a'iwn space or
   period of time, lifetime, age; akin to L. aevum. See Age.]
   1. An immeasurable or infinite space of time; eternity; a
      long space of time; an age.
      [1913 Webster]

            The eons of geological time.          --Huxley.
      [1913 Webster]

   2. (Gnostic Philos.) One of the embodiments of the divine
      attributes of the Eternal Being.
      [1913 Webster]

            Among the higher [ae]ons are Mind, Reason, Power,
            Truth, and Life.                      --Am. Cyc.
      [1913 Webster]

   Note: Eons were considered to be emanations sent forth by God
         from the depths of His grand solitude to fulfill
         various functions in the material and spiritual
         universe.
         [1913 Webster]

WordNet (r) 3.0 (2006):

aeon
    n 1: (Gnosticism) a divine power or nature emanating from the
         Supreme Being and playing various roles in the operation of
         the universe [syn: eon, aeon]
    2: the longest division of geological time [syn: eon, aeon]
    3: an immeasurably long period of time; "oh, that happened eons
       ago" [syn: eon, aeon]