the english word 'tsar' is a direct borrowing from the russian 'tsar', which itself descends from the latin title 'caesar', used as a synonym for emperor. the latin name 'caesar', originally a family name, became an imperial title adopted by roman emperors and later byzantine rulers. this title traveled into slavic languages via the byzantine greek 'kaisar', evolving phonetically into 'tsar' to denote a supreme ruler, specifically the emperor of russia, and later metaphorically for any person wielding autocratic power.

this word is a loanword adopted as a single, unanalyzable unit into english from russian.