noun The act of calling into question or challenging the accuracy or propriety of something.
noun A demonstration in a court of law, or before another finder of fact, that a witness was ingenuine before, and is therefore less likely to tell the truth now.
noun An accusation that a person has committed a crime against the state, such as treason.
noun The act of impeaching or charging a public official with misconduct, especially if serious, often with the aim of having the official dismissed from office.