General lack of intelligence:
* Un-: This is the most basic prefix for negation, but it's not as strong as some others. "Unintelligent" is the most direct option.
* Non-: This emphasizes a lack of something, like "non-intellectual" or "non-academic".
* In-: This often indicates a lack of something desirable, like "incompetent" or "inept".
More specific contexts:
* Un-: "Unsophisticated" or "uninformed" imply a lack of knowledge or social graces.
* Dis-: "Discerning" implies a lack of good judgment or critical thinking.
* Anti-: This suggests opposition to intellectual pursuits, like "anti-intellectual".
Other options:
* Slow: "Slow-witted" implies a delay in processing information.
* Clueless: This implies a complete lack of understanding.
* Stupid: This is the most blunt and negative word.
The best choice depends on the specific situation and the desired level of formality.