unintelligent

This term carries a strong negative connotation, often implying a permanent lack of mental capacity or a severe failure in judgment. It is more clinical and direct than words like silly or foolish, which can sometimes be used affectionately or to describe a temporary lapse in reason. When describing a person, it suggests a cognitive deficit, whereas when describing an action or decision, it emphasizes a lack of foresight or strategic thinking. It is typically used in formal or critical contexts to denote a deficiency in intellectual power.