Antonyms are words that are opposite in meaning to each other. When it comes to the word "un-intelligent", there are various antonyms that represent its opposite meaning. Firstly, we can use "smart" or "intelligent" as an antonym as it denotes having a high IQ or intelligence. Other antonyms could be "clever", which means having quick wit and creative problem-solving skills, or "astute", which represents having the ability to make shrewd and insightful decisions. There are also words like "knowledgeable", "perceptive", "wise", or "brilliant" that can serve as antonyms. All of these antonyms represent a different level of intellectual prowess, and using them can help to emphasize clear communication and precise language.