czar (n.)

the common title of the emperor of Russia, 1550s, from Russian tsar, from Old Slavic tsesari, from Gothic kaisar, from Greek kaisar, from Latin Caesar. First adopted by Russian emperor Ivan IV, 1547.

The spelling with cz- is against the usage of all Slavonic languages; the word was so spelt by Herberstein, Rerum Moscovit. Commentarii, 1549, the chief early source of knowledge as to Russia in Western Europe, whence it passed into the Western Languages generally; in some of these it is now old-fashioned; the usual Ger. form is now zar; French adopted tsar during the 19th c. This also became frequent in English towards the end of that century, having been adopted by the Times newspaper as the most suitable English spelling. [OED]

The Germanic form of the word also is the source of Finnish keisari, Estonian keisar. The transferred sense of "person with dictatorial powers" is first recorded 1866, American English, initially in reference to President Andrew Johnson. The fem. czarina is 1717, from Italian czarina, from Ger. Zarin, fem. of Zar "czar." The Russian fem. form is tsaritsa. His son is tsarevitch, his daughter is tsarevna.