master has 27 distinct synonyms spread across 13 of its 15 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an artist of consummate skill
“a master of the violin”
a person who has general authority over others
directs the work of others
presiding officer of a school
an original creation (i.e., an audio recording) from which copies can be made
an officer who is licensed to command a merchant ship
someone who holds a master's degree from academic institution
an authority qualified to teach apprentices
key that secures entrance everywhere
be or become completely proficient or skilled in
“She mastered Japanese in less than two years”
Synonyms, antonyms and the broader and narrower relations for master come from Princeton University’s WordNet. Full sources and licences.