It is the opposite of "sharp mind". See mind, obtuse, acute.
You want to say intransigent radical, stubborn, stubborn, fanatic opposition.
That it is limited to understand
Form of thought foolish, closed and irrational.
Applies to the person who is slow in understanding things simpler. Clumsy, slow of understanding.In mind obtuse, lyrics, or to stick tip penetrates. (Spanish proverb )