The possessor of a master's degree.
Master; sir: a title used in the Middle Ages, given to a person in authority, or to one having a licence from a university to teach philosophy and the liberal arts.
A person who settles a dispute.
An expert who judges the manuscript of an article or book to decide if it should be published.
An umpire or judge; an official who makes sure the rules are followed during a game.
A person who writes a letter of reference or provides a reference by phone call for someone. US English: reference.
To act as a referee.