simpleminded

or sim·ple-mind·ed

[ sim-puhl-mahyn-did, -mahyn- ]
/ ˈsɪm pəlˈmaɪn dɪd, -ˌmaɪn- /

adjective

free of deceit or guile; artless or unsophisticated.
lacking in mental acuteness or sense.
mentally deficient.

Origin of simpleminded

First recorded in 1735–45; simple + minded

Related forms

sim·ple·mind·ed·ly, adverbsim·ple·mind·ed·ness, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019