Birdbrain is a slang word used to describe someone who is perceived as stupid or slow-witted. The antonyms for birdbrain include clever, smart, wise, intelligent, knowledgeable, and sharp-witted. A clever person is someone who is able to solve problems quickly and efficiently. A smart person is someone who is well-informed and able to make sound judgments. A wise person is someone who possesses deep knowledge and understanding. An intelligent person is someone who has the ability to acquire and apply knowledge and skills. Knowledgeable people are well-informed about various subjects. A sharp-witted person has the ability to think quickly and make snap judgments.