master

noun | mas·ter

1. a : the owner of a slave

   b : employer — compare servant

   c : principal 1a

2. : an officer of the court appointed (as under Federal Rule of Civil Procedure 53) to assist a judge in a particular case by hearing and reporting on the case, sometimes by making findings of fact and conclusions of law, and by performing various related functions

   Note: Under the Federal Rules of Civil Procedure, a master may be a magistrate or else may be a person with some special expertise in the matter. The word master as used in the Federal Rules encompasses a referee, an auditor, an examiner, and an assessor. If the master makes findings of fact, they are reviewable de novo by the court except when the parties have stipulated that the findings will be reviewed for clear error or that the master's findings are to be final.

adjective

1. : being the principal or controlling one : governing a number of subordinate like things a master insurance policy