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Synonyms for Master (same or very similar meaning)

WordNet sense 1 (a combatant who is able to defeat rivals):
victor, superior

WordNet sense 2 (a person who has general authority over others):
lord, overlord

WordNet sense 3 (an officer who is licensed to command a merchant ship):
captain, skipper, sea captain

WordNet sense 4 (an authority qualified to teach apprentices):
professional

WordNet sense 5 (an artist of consummate skill):
maestro

WordNet sense 6 (presiding officer of a school):
headmaster, schoolmaster

WordNet sense 7 (key that secures entrance everywhere):
passkey, passe-partout, master key

WordNet sense 8 (an original creation (i.e., an audio recording) from which copies can be made):
original, master copy

WordNet sense 9 (have dominance or the power to defeat over):
dominate

WordNet sense 10 (get on top of; deal with successfully):
overcome, subdue, surmount, get over

WordNet sense 11 (be or become completely proficient or skilled in):
get the hang

WordNet sense 12 (have a firm understanding or knowledge of; be on top of):
control


From the ODE community, based on WordNetadd/edit