Tsar, also spelled czar, or tzar or csar, is a title used to designate East and South Slavic monarchs or supreme rulers of Eastern Europe, originally the Bulgarian monarchs from 10th century onwards, much later a title for two rulers of the Serbian State, and from 1547 the supreme ruler of the Tsardom of Russia and the Russian Empire. In this last capacity it lends its name to a system of government, 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, 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.