IPA: //ˈmæstərfəl.nəs//
KK: /ˈmæstərfəl/
The quality of being very skilled or in control, often in a way that shows great ability or confidence.
Her masterfulness in negotiation helped secure the best deal for the company.
Masterfulness → It is formed from "master" (from Old French *maistre*, meaning one who has control or authority) and "-fulness" (meaning the quality of being full of). The word "masterfulness" refers to the quality of being in control or having authority.
Think of someone who is a 'master' (meaning they have control) and the '-fulness' indicating the quality of that mastery. This helps you remember that 'masterfulness' means the quality of being in control.