Noah Webster's New International Dictionary of the English Language

1. (v. t.) To hinder; to impede; to prevent.

2. (v. t.) 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. (v. t.) Hence, to charge with impropriety; to dishonor; to bring discredit on; to call in question; as, to impeach one's motives or conduct.

4. (v. t.) To challenge or discredit the credibility of, as of a witness, or the validity of, as of commercial paper.

5. (n.) Hindrance; impeachment.