If you mastermind a difficult or complicated activity, you plan it in detail and then make sure that it happens successfully. The finance minister will continue to mastermind Poland's economic reform
The mastermind behind a difficult or complicated plan, often a criminal one, is the person who is responsible for planning and organizing it. He was the mastermind behind the plan to acquire the explosives. someone who plans and organizes a complicated operation, especially a criminal operation. to think of, plan, and organize a large, important, and difficult operation