The phrase "in equilibrium" can be replaced with various synonyms depending on the context. For instance, one may use "balanced" to describe a system that is in stable equilibrium, "steady-state" for a process that remains constant over time, or "harmonious" for a situation where all the elements are in perfect balance with each other. Additionally, "quiescent" and "calm" can also be used to describe a state of rest or repose. "Equilibrated" is another synonym that implies a balance or stability in a system or situation. Overall, there are numerous synonyms for "in equilibrium" that can be used to describe different types of stability and balance in various contexts.