The Collaborative International Dictionary of English v.0.48:

Season \Sea"son\, v. t. [imp. & p. p. Seasoned; p. pr. & vb.
   n. Seasoning.]
   1. To render suitable or appropriate; to prepare; to fit.
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            He is fit and seasoned for his passage. --Shak.
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   2. To fit for any use by time or habit; to habituate; to
      accustom; to inure; to ripen; to mature; as, to season one
      to a climate.
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   3. Hence, to prepare by drying or hardening, or removal of
      natural juices; as, to season timber.
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   4. To fit for taste; to render palatable; to give zest or
      relish to; to spice; as, to season food.
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   5. Hence, to fit for enjoyment; to render agreeable.
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            You season still with sports your serious hours.
                                                  --Dryden.
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            The proper use of wit is to season conversation.
                                                  --Tillotson.
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   6. To qualify by admixture; to moderate; to temper. "When
      mercy seasons justice." --Shak.
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   7. To imbue; to tinge or taint. "Who by his tutor being
      seasoned with the love of the truth." --Fuller.
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            Season their younger years with prudent and pious
            principles.                           --Jer. Taylor.
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   8. To copulate with; to impregnate. [R.] --Holland.
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WordNet (r) 3.0 (2006):

seasoned
    adj 1: aged or processed; "seasoned wood" [ant: unseasoned]
    2: rendered competent through trial and experience; "a seasoned
       traveler"; "veteran steadiness"; "a veteran officer" [syn:
       seasoned, veteran(a)]

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "seasoned":
   acclimated, acclimatized, accommodated, accustomed, adapted,
   adjusted, aged, blase, brisk, burning, case-hardened, conditioned,
   cosmopolitan, cosmopolite, curried, developed, established,
   experienced, familiarized, full-blown, full-fledged, full-grown,
   fully developed, habituated, hardened, hedged, hedged about,
   high-seasoned, hot, hot as pepper, in full bloom, inured, knowing,
   leavened, limited, lively, long-standing, maturated, mature,
   matured, mellow, mellowed, mitigated, modified, modulated,
   naturalized, nippy, not born yesterday, old, old-time, orientated,
   oriented, peppery, practical, practiced, prepared, qualified, racy,
   restricted, ripe, ripened, run-in, sagacious, skilled, snappy,
   softened, sophisticated, spiced, spicy, steeled, tangy, tempered,
   toughened, trained, tried, tried and true, used to, versed, vet,
   veteran, well-versed, with a kick, wont, wonted, world-wise,
   worldly, worldly-wise, zestful, zesty, zippy