(1) To prove false or discredit the testimony of a witness or a party. It is any evidence that tends to show that the testimony of a person who testifies is not credible and should not be believed. (2) The process by which a public official is charged with a crime that results in their removal from office, for example, a President who lies under oath with the penalty of perjury.
Law Dictionary – Alternative Legal Definition
To accuse; to charge a liability upon; to sue.
To dispute, disparage, deny, or contradict; as, to impeach a judgment or decree; or as used In the rule that a jury cannot “impeach their verdict”. To proceed against a public officer for crime or misfeasance, before a proper court by the presentation of a written accusation called “articles of impeachment”. In the law of evidence. To call in question the veracity of a witness, by means of evidence adduced for that purpose.