mastermind UK /ˈmɑː.stə.mʌɪnd/US /ˈmæs.tɚˌmaɪnd/noun 2verb 1forms 3 noun2 •A person with an extraordinary intellect or skill that is markedly superior to their peers.At long intervals some master-minds appeared, looking upon each advance in practical science as a retro-gradation in the true utility. — 1840 •A person responsible for the highest level of planning and execution of a major operation.The first was with none other than Khalid Sheikh Mohammad (KSM), mastermind of the 9/11 attacks. — 2007 verb1 •To plan or execute (a project) in the role of mastermind. formsmasterminded · masterminding · masterminds