The phrase "being in the power of" means to be under the control or authority of someone or something. There are many synonyms that can be used to describe this situation, such as being at the mercy of, being under someone's thumb, being under someone's control, being subjected to, being beholden to, being subservient to, being dependent on, and being influenced by. All of these terms convey the same idea of being subordinate to a more powerful force, whether it be a person, a government, or a situation. Understanding these synonyms can help to illustrate the nuances of power dynamics and how they impact our everyday lives.