As nouns the difference between magi and magister

is that magi is plural of lang=en while magister is master; sir: -- a title of the Middle Ages, given to a person in authority, or to one having a license from a university to teach philosophy and the liberal arts.

As a proper noun Magi

is the wise men that met the baby Jesus at the Epiphany (traditionally considered to be three in number and usually named Melchior, Caspar and Balthazar).