Antonyms, also known as opposites, are words that have an opposite meaning to another word. For the word "not notably," the antonyms could include words such as "remarkably," "significantly," "distinctly," "prominently," and "obviously." These words suggest that something is notable or noteworthy, whereas "not notably" implies that it is not. By using antonyms, we can differentiate between things that are important and those that are not. For example, we might say that while the performance was not notably good, it was not notably bad either. Using antonyms helps provide a more nuanced understanding of language and the world around us.