someone whose job is to protect a place or person.——朗文当代大辞典

One who keeps, protects, or defends; a protector, defender; spec. one of a guard (sense 9), a sentry, sentinel; a warder in a prison or other place of detention (chiefly U.S.). Also with preceding n. denoting the object defended, as coast-guard n., telegraph guard, etc.——牛津当代大辞典  @en