The Latin title has the meaning of "king, ruler" (monarch). It is derived from Proto-Indo-European *hâÂÂrá¸Âõs. Its cognates include Sanskrit rÃÂjan, Gothic reiks, and Old Irish rÃÂ, etc. Its Greek equivalent is (), "leader, ruler, chieftain".
The chief magistrate of the Roman Kingdom was titled Rex Romae (King of Rome).