From the Latin vocabulary word meaning ‘king’. This was not used as a personal name in Latin of the classical or Christian periods, and its adoption as a given name seems to have been a 19th-century innovation. Its popularity was increased by the fame of the British actor Rex Harrison (1908–90), who was christened Reginald Carey.
German: occupational name or status name from the German word Knapp(e), a variant of Knabe ‘young unmarried man’. In the 15th century this spelling acquired the separate, specialized meanings ‘servant’, ‘apprentice’, or ‘miner’.