2 English words descend from Proto-Germanic *kaisaraz, most common first.
kaiserAn emperor of a German-speaking country, particularly the Holy Roman Empire (962–1806), the Austrian Empire/Austria-Hungary (1806–1918), or the German Empire (1871–1918) — often specifically Wilhelm II.
tsarAn emperor of Russia (1547 to 1917) and of some South Slavic states.