the female ruler of a country.——朗文当代大辞典

 the wife of a king.——朗文当代大辞典

A woman, esp. a noblewoman; a wife, esp. of an important man.——牛津当代大辞典

The wife or consort of a king. Frequently with the, as a title.——牛津当代大辞典

A female ruler of an independent state, people, etc., esp. one who inherits the position by right of birth; a female sovereign. Frequently with the, as a title.——牛津当代大辞典  @en