From Longman Dictionary of Contemporary Englishnumbskullnumb‧skull, numskull /ˈnʌmskʌl/ noun [countable] informal STUPID/NOT INTELLIGENTa very stupid person SYN idiot Look what you’ve done now, you numbskull!
Examples from the Corpus
numbskull• Yet somehow the delusion has taken hold that a commitment to democratic self-rule means coaxing apathetic numbskulls into voting.• She'd breezed through the courts, faking numbskull stupidity, and come out clean. 