The Collaborative International Dictionary of English v.0.48:

Anon \A*non"\, adv. [OE. anoon, anon, anan, lit., in one
   (moment), fr. AS. on in + [=a]n one. See On and One.]
   1. Straightway; at once. [Obs.]
      [1913 Webster]

            The same is he that heareth the word, and anon with
            joy receiveth it.                     --Matt. xiii.
                                                  20.
      [1913 Webster]

   2. Soon; in a little while.
      [1913 Webster]

            As it shall better appear anon.       --Stow.
      [1913 Webster]

   3. At another time; then; again.
      [1913 Webster]

            Sometimes he trots, . . . anon he rears upright.
                                                  --Shak.
      [1913 Webster]

   Anon right, at once; right off. [Obs.] --Chaucer.

   Ever and anon, now and then; frequently; often.
      [1913 Webster]

            A pouncet box, which ever and anon
            He gave his nose.                     --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

anon.
    adj 1: having no known name or identity or known source;
           "anonymous authors"; "anonymous donors"; "an anonymous
           gift" [syn: anonymous, anon.] [ant: onymous]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "anon":
   after a time, after a while, afterward, afterwards, again,
   at another time, at that moment, at that time, before long,
   betimes, by and by, by destiny, directly, ere long, fatally,
   hopefully, imminently, in a moment, in a while, in aftertime,
   in due course, in due time, in that case, in the future, later,
   on that occasion, predictably, presently, probably, proximo,
   shortly, soon, then, thereat, tomorrow, when