IPA: /ˈmæstəri/
KK: /ˈmæstəri/
Complete control or skill in a particular area or subject.
His mastery of the piano allowed him to perform complex pieces effortlessly.
Mastery → It is formed from "master" (from Old French *maistre*, meaning one who has control or authority) and "-y" (a suffix used to form nouns indicating a state or condition). The word "mastery" refers to the state of having control or expertise in a particular area.
Think of someone who is a 'master' in their field, showing that 'mastery' means being in a state of control or expertise.