"Addlebrains" is a slang term used to describe someone who is foolish or confused. Its antonyms would include adjectives such as intelligent, bright, clever, astute, and sharp-witted. These words suggest a person who is smart, insightful, and capable of understanding complex concepts. Other antonyms for "addlebrains" might include words like knowledgeable, wise, savvy, and shrewd. These words imply a level of expertise and understanding that is lacking in someone who is considered to be addlebrained. When you use these antonyms, you are conveying a sense of respect and admiration for a person's intellectual abilities, rather than denigrating them.