The Collaborative International Dictionary of English v.0.48:

Confirm \Con*firm"\, v. t. [imp. & p. p. Confrmed; p. pr. &
   vb. n. Confirming.] [OE. confermen, confirmen, OF.
   confermer, F. confirmer, fr. L. confirmare; con- + firmare to
   make firm, fr. firmus firm. See Firm.]
   1. To make firm or firmer; to add strength to; to establish;
      as, health is confirmed by exercise.
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            Confirm the crown to me and to mine heirs. --Shak.
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            And confirmed the same unto Jacob for a law. --Ps.
                                                  cv. 10.
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   2. To strengthen in judgment or purpose.
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            Confirmed, then, I resolve
            Adam shall share with me in bliss or woe. --Milton.
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   3. To give new assurance of the truth of; to render certain;
      to verify; to corroborate; as, to confirm a rumor.
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            Your eyes shall witness and confirm my tale. --Pope.
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            These likelihoods confirm her flight. --Shak.
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   4. To render valid by formal assent; to complete by a
      necessary sanction; to ratify; as, to confirm the
      appoinment of an official; the Senate confirms a treaty.
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            That treaty so prejudicial ought to have been
            remitted rather than confimed.        --Swift.
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   5. (Eccl.) To administer the rite of confirmation to. See
      Confirmation, 3.
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            Those which are thus confirmed are thereby supposed
            to be fit for admission to the sacrament. --Hammond.

   Syn: To strengthen; corroborate; substantiate; establish;
        fix; ratify; settle; verify; assure.
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WordNet (r) 3.0 (2006):

confirm
    v 1: establish or strengthen as with new evidence or facts; "his
         story confirmed my doubts"; "The evidence supports the
         defendant" [syn: confirm, corroborate, sustain,
         substantiate, support, affirm] [ant: contradict,
         negate]
    2: strengthen or make more firm; "The witnesses confirmed the
       victim's account" [syn: confirm, reassert]
    3: make more firm; "Confirm thy soul in self-control!"
    4: support a person for a position; "The Senate confirmed the
       President's candidate for Secretary of Defense"
    5: administer the rite of confirmation to; "the children were
       confirmed in their mother's faith"