Smart as a whip is a phrase commonly used to describe someone who is intelligent, astute, quick-witted, and clever. The phrase has a positive connotation, so the antonyms would be words that have negative connotations. Some antonyms for smart as a whip could be dull, unintelligent, slow-witted, foolish, naive, or clueless. These words do not necessarily mean that someone is unintelligent, but they show the opposite traits of being clever, astute, or sharp. It's important to note that just because someone may not be smart as a whip, it doesn't mean they aren't competent or capable.