The term "a bit thick" is often used to refer to someone who is dull or not very intelligent. Antonyms for this phrase include words like clever, bright, sharp, and intelligent. Other antonyms that could be used to describe a person who is not "a bit thick" might include words like quick-witted, nimble-minded, astute, acute, shrewd, or insightful. These antonyms describe someone who is able to think quickly and respond appropriately to various situations, demonstrating a high level of intelligence or mental agility. By using these antonyms, we can describe someone as being the opposite of "a bit thick", highlighting their intelligence and abilities, rather than their shortcomings.