The Collaborative International Dictionary of English v.0.48:

Impeach \Im*peach"\, v. t. [imp. & p. p. Impeached; p. pr. &
   vb. n. Impeaching.] [OE. empeechier to prevent, hinder,
   bar, F. emp[^e]cher, L. impedicare to entangle; pref. im- in
   + pedica fetter, fr. pes, pedis, foot. See Foot, and
   Appeach, Dispatch, Impede.]
   1. To hinder; to impede; to prevent. [Obs.]
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            These ungracious practices of his sons did impeach
            his journey to the Holy Land.         --Sir J.
                                                  Davies.
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            A defluxion on my throat impeached my utterance.
                                                  --Howell.
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   2. To charge with a crime or misdemeanor; to accuse;
      especially to charge (a public officer), before a
      competent tribunal, with misbehavior in office; to cite
      before a tribunal for judgment of official misconduct; to
      arraign; as, to impeach a judge. See Impeachment.
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   3. Hence, to charge with impropriety; to dishonor; to bring
      discredit on; to call in question; as, to impeach one's
      motives or conduct.
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            And doth impeach the freedom of the state. --Shak.
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   4. (Law) To challenge or discredit the credibility of, as of
      a witness, or the validity of, as of commercial paper.
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   Note: When used in law with reference to a witness, the term
         signifies, to discredit, to show or prove unreliable or
         unworthy of belief; when used in reference to the
         credit of witness, the term denotes, to impair, to
         lessen, to disparage, to destroy. The credit of a
         witness may be impeached by showing that he has made
         statements out of court contradictory to what he swears
         at the trial, or by showing that his reputation for
         veracity is bad, etc.

   Syn: To accuse; arraign; censure; criminate; indict; impair;
        disparage; discredit. See Accuse.
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