Keen-witted means having a sharp and clever mind. The antonyms for the word are dull-witted, slow-witted, and stupid. Dull-witted refers to someone who lacks intelligence or is not quick to grasp things. Slow-witted means someone who takes a long time to understand or learn something. Stupid means someone who is lacking in intelligence or is unable to comprehend things easily. These antonyms indicate a lack of intelligence or mental acuity. Keen-witted people are quick-minded and able to think logically and creatively, while dull or slow-witted people struggle with problem solving and critical thinking.