1. also tsar or tzar (zär, tsär) A male monarch or emperor, especially one of the emperors who ruled Russia until the revolution of 1917.
2. A person having great power; an autocrat: "the square-jawed, ruddy complacency of Jack Farrell, the czar of the Fifteenth Street police station" (Ernest Hemingway).
3. Informal An appointed official having special powers to regulate or supervise an activity: a racetrack czar; an energy czar.

Usage Note: The word czar can also be spelled tsar. Czar is the most common form in American usage and the one nearly always employed in the extended senses "any tyrant" or informally, "one in authority." But tsar is preferred by most scholars of Slavic studies as a more accurate transliteration of the Russian and is often found in scholarly writing with reference to one of the Russian emperors.