From Longman Dictionary of Contemporary Englishnincompoopnin‧com‧poop /ˈnɪŋkəmpuːp/ noun [countable] old-fashioned STUPID/NOT INTELLIGENTa stupid person
Examples from the Corpus
nincompoop• It was sheer bloody hell listening to all those fatuous nincompoops saying what a great guy you are.Origin nincompoop (1700-1800) ninny + nicompoop “stupid person” ((1600-1700)) 