From Longman Dictionary of Contemporary Englishnitwitnit‧wit /ˈnɪt-wɪt/ noun [countable] informal STUPID/NOT INTELLIGENTa silly person
Examples from the Corpus
nitwit• Given the collection of egomaniacs and nitwits who represent the Cowboys, this was quite refreshing.• Good, bright, yet for ever passed over and having to report to some nitwit with the right school connections and bloodlines.Origin nitwit (1900-2000) Probably from German dialect nit “not” + English wit 