(role-playing games) A person conducting a role-playing game, generally responsible for controlling all beings and processes other than the players, either individually or as part of a team.

(nautical) A seaman who has qualified to be a captain of a merchant ship

A thesis submitted for a master's degree.

plural of master's thesis

plural of master sergeant

(UK, Navy) A warrant officer or chief petty officer responsible for discipline aboard a naval ship.

(Canada, Navy) A non-commissioned officer in the Canadian Forces Maritime Command, ranking above leading seaman and below petty officer second class.

plural of master seaman

(role-playing games) A game master in Dungeons & Dragons games.

plural of master's degree