Mastermind/ˈmæstərmaɪnd/ Definition 1 of 2Pro Tip 1/3Positive Connotation Often implies a person has exceptional intelligence or skill. The chess player was a mastermind in foreseeing his opponent's moves. Pro Tip 2/3Not Always Lawful Can refer to someone planning legal or illegal activities. The notorious thief was the mastermind of the elaborate bank heist. Pro Tip 3/3Complex Tasks Used when referring to complicated or detailed projects. She was the mastermind behind the school's annual science fair.