The Collaborative International Dictionary of English v.0.48:

Magister \Ma*gis"ter\, n. [L. See Master.]
   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.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

MAGISTER. A master, a ruler, one whose learning and position makes him
superior to others, thus: one who has attained to a high degree, or
eminence, in science and literature, is called a master; as, master of arts.