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.]
These ungracious practices of his sons did impeach
his journey to the Holy Land. --Sir J.
A defluxion on my throat impeached my utterance.
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.
3. Hence, to charge with impropriety; to dishonor; to bring
discredit on; to call in question; as, to impeach one's
motives or conduct.
And doth impeach the freedom of the state. --Shak.
4. (Law) To challenge or discredit the credibility of, as of
a witness, or the validity of, as of commercial paper.
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.
Moby Thesaurus II by Grady Ward, 1.0:
18 Moby Thesaurus words for "impeached":
accused, arraigned, blamed, charged, cited, denounced, implicated,
impugned, in complicity, incriminated, inculpated, indicted,
involved, reproached, tasked, taxed, under attack, under fire