"Sealed shut" can be considered as an antonym for "broke open". It means to tightly close or block an object's entrance or exit. Another antonym that can be used is "locked up", which refers to something that has been closed and secured using a locking mechanism. This word is commonly used to describe locked doors, safes and other storage containers. Similarly, "sealed" can also be used as an antonym which conveys an action of closing or covering an object tightly with a material, such as plastic or tape. It is important to have a clear understanding of antonyms to avoid using contradictory words in writing or communication.