czar

Czar traces back to Latin Caesar, borrowed into Proto-Germanic as *kaisaraz, then into Proto-Slavic as *cěsařь, which passed into Old East Slavic as цѣсарь and цьсарь, and finally into Russian as царь.

The English spelling czar is actually older than the now-more-common tsar, first appearing in Sigismund von Herberstein's 1549 book Notes on Muscovite Affairs. Czar was later supplanted by the tsar spelling in the 19th century.

Czar shares its ultimate root with Caesar itself, having descended from that very name through Germanic and Slavic borrowings.