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.]
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            The same is he that heareth the word, and anon with
            joy receiveth it.                     --Matt. xiii.
                                                  20.
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   2. Soon; in a little while.
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            As it shall better appear anon.       --Stow.
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   3. At another time; then; again.
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            Sometimes he trots, . . . anon he rears upright.
                                                  --Shak.
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   Anon right, at once; right off. [Obs.] --Chaucer.

   Ever and anon, now and then; frequently; often.
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            A pouncet box, which ever and anon
            He gave his nose.                     --Shak.
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WordNet (r) 3.0 (2006):

anon
    adv 1: at another time; "ever and anon"
    2: (old-fashioned or informal) in a little while; "see you anon"

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