Tsar /zɑːr/ (Old Church Slavonic: ц︢рь [usually written thus with a title] or цар, цaрь) or czar is a title used to designate certain Slavic monarchs or supreme rulers. As a system of government in the Tsardom of Russia and Russian Empire, it is known as Tsarist autocracy, or Tsarism. The term is derived from the Latin word Caesar, which was intended to mean "Emperor" in the European medieval sense of the term—a ruler with the same rank as a Roman emperor, with-holding it by the approval of another emperor or a supreme ecclesiastical official (the Pope or the Ecumenical Patriarch)—but was usually considered by western Europeans to be equivalent to king, or to be somewhat in between a royal and imperial rank.