master

a combatant who is able to defeat rivals

an officer who is licensed to command a merchant ship

an artist of consummate skill

“a master of the violin”

have a firm understanding or knowledge of; be on top of

most important element

“the master bedroom”

directs the work of others

someone who holds a master's degree from academic institution

get on top of; deal with successfully

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”