Antonyms for the term "break open" include terms like "seal," "close," "lock," "fasten," or "shut." These words are often used to refer to actions that involve closing or securing something, rather than opening it. For example, you might "seal" a container or "lock" a door to keep things inside safe and secure. Similarly, you might "fasten" a lid or "shut" a window to keep out unwanted air, light, or noise. The antonyms for "break open" are important to know when talking about actions that involve opening, closing, or securing things in different contexts.