Antonyms, also known as opposite words, are an important part of language learning. The word "open" has several antonyms. The first one is "closed," which means something is not open or accessible. The second one is "shut," which means something is firmly closed or fastened. The third antonym is "locked," which means something is secured with a key or lock. Another antonym for "open" is "narrow," which means something has a small width or is tightly confined. Additionally, "sealed" is another antonym for "open" which means something is closed or covered securely. Understanding antonyms is essential for building a wide range of vocabulary in everyday language.