Thick-skulled is a term used to describe someone who is stubborn, slow-witted or hard to teach. Its antonyms, then, would be words that describe the opposite traits: intelligent, open-minded or quick-witted. Some options for antonyms of thick-skulled include bright, perceptive, sharp, savvy, insightful, responsive and receptive. Another possible antonym could be malleable, which would suggest someone who is easily molded or adaptable. Ultimately, the antonyms of thick-skulled are words that reflect intellectual agility, emotional intelligence and a willingness to learn and listen to others.