The Collaborative International Dictionary of English v.0.48:

Ascertain \As`cer*tain"\, v. t. [imp. & p. p. Ascertained; p.
   pr. & vb. n. Ascertaining.] [OF. acertener; a (L. ad) +
   certain. See Certain.]
   1. To render (a person) certain; to cause to feel certain; to
      make confident; to assure; to apprise. [Obs.]
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            When the blessed Virgin was so ascertained. --Jer.
                                                  Taylor.
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            Muncer assured them that the design was approved of
            by Heaven, and that the Almighty had in a dream
            ascertained him of its effects.       --Robertson.
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   2. To make (a thing) certain to the mind; to free from
      obscurity, doubt, or change; to make sure of; to fix; to
      determine. [Archaic]
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            The divine law . . . ascertaineth the truth.
                                                  --Hooker.
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            The very deferring [of his execution] shall increase
            and ascertain the condemnation.       --Jer. Taylor.
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            The ministry, in order to ascertain a majority . . .
            persuaded the queen to create twelve new peers.
                                                  --Smollett.
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            The mildness and precision of their laws ascertained
            the rule and measure of taxation.     --Gibbon.
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   3. To find out or learn for a certainty, by trial,
      examination, or experiment; to get to know; as, to
      ascertain the weight of a commodity, or the purity of a
      metal.
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            He was there only for the purpose of ascertaining
            whether a descent on England was practicable.
                                                  --Macaulay.
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WordNet (r) 3.0 (2006):

ascertained
    adj 1: discovered or determined by scientific observation;
           "variation in the ascertained flux depends on a number of
           factors"; "the discovered behavior norms"; "discovered
           differences in achievement"; "no explanation for the
           observed phenomena" [syn: ascertained, discovered,
           observed]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "ascertained":
   actual, appreciated, apprehended, assured, attested, authenticated,
   borne out, categorically true, certain, certified,
   circumstantiated, comprehended, conceived, confirmed, corroborated,
   decided, demonstrated, determinate, determined, discerned,
   documentary, down pat, effectual, established, factual, fixed,
   grasped, guaranteed, historical, in the bag, known, made sure,
   nailed down, not in error, objectively true, on ice, open-and-shut,
   pat, perceived, prehended, proved, proven, real, realized,
   recognized, secure, seized, set, settled, shown, stated,
   substantiated, sure-enough, tested, tried, true, true as gospel,
   truthful, unconfuted, undenied, understood, undoubted, unerroneous,
   unfallacious, unfalse, unmistaken, unquestionable, unrefuted,
   validated, veracious, verified, veritable, warranted