Keeping something in is a common concept that can be replaced by several different synonyms. One of the most common synonyms for "keep in" is "retain." Retaining something usually means holding onto it, whether it's information or an object. Alternatively, a synonym that could be used is "maintain." Maintaining something means continuing to hold onto it, or perhaps even taking steps to keep it in good condition. Another synonym to consider is "preserve," which implies keeping something safe and sound, especially if it's valuable or delicate. Ultimately, there are many different ways to describe what it means to "keep in," and the right synonym will depend on the specific context of the situation.