de·par·ture / diˈpärchər/ • n. the action of leaving, typically to start a journey: the day of departure | she made a hasty departure. ∎ a deviation from an accepted, prescribed, or traditional course of action or thought: a departure from their usual style. ∎ Naut. the east–west distance between two points, esp. as traveled by a ship or aircraft and expressed in miles.