sim·ple·mind·ed 
/ˌsɪmpəlˈmaɪndəd/ adjective
/ˌsɪmpəlˈmaɪndəd/ adjective [more simpleminded; most simpleminded] 1 : not very intelligent
▪ a superstitious and very simpleminded man ▪ He took a simpleminded approach to the problem. 2 : having or showing a lack of good sense or judgment
▪ a simpleminded [=stupid, silly] mistake
▪ a superstitious and very simpleminded man ▪ He took a simpleminded approach to the problem.
▪ a simpleminded [=stupid, silly] mistake
