The etymology of "master" according to Wiktionary:

From Middle English maister, mayster, meister, from Old English mǣster, mæġster, mæġester, mæġister, magister (“master”), from Latin magister (“chief, teacher, leader”), from Old Latin magester, from Proto-Indo-European *méǵh₂s, (as in magnus (“great”)) + -ester/-ister