Definition - a calling to account for some high crime or offense before a competent tribunal; especially, the arraignment (as of a public official) for misconduct while in office
Impeachment has a variety of closely related meanings in addition to the definition provided above. These include obsolete senses (such as “hindrance, obstruction” and “injury or damage”) and broadened ones (such as “conviction of misconduct and usually removal of office”). The legal sense in which impeachment is applied to governmental proceedings in the United States typically refers to a step in the process of potentially removing an official from office, and does not describe the actual removal.
The relevant section of the United States Constitution (Article 2, Section 4) states that “The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.” Impeach may function as both a verb and a noun (the noun sense, meaning “charge, impeachment”) is now obsolete. The adjective, should you be looking for one, is impeachable (“capable of being impeached”).
And as to the Question, Whether an House of Parliament can commit Treason? If they depart from that Allegiance which they have sworn, at their first meeting, they are impeachable for it.
— Henry Vane, The tryal of Sir Henry Vane, 1662