Wiktionary
unbright
a. Not bright; of limited intellect.
Usage examples of "unbright".
Ideally the largest creatures should be the smartest, but in fact these had been dinosaurs and whales and other relatively unbright forms.
You're more bugged by the possibility that I'm treating you as unbright and distractable than you are about a resident's inability to come right out and openly exercise her right to refuse to answer an incredibly private and drug-unrelated question.