slow-witted
From Longman Dictionary of Contemporary Englishslow-wittedˌslow-ˈwitted adjective STUPID/NOT INTELLIGENTnot good at understanding things SYN stupidExamples from the Corpusslow-witted• No doubt such people must have seemed slow-witted.• His misery made him slow-witted and careless and he was ashamed of the part he had played at the warren.• He had a reputation for being a bit slow-witted but it didn't perturb him in the least.