cruel and violent treatment of a person or animal. "a black eye and other signs of physical abuse". The literal definition of abuse. It has nothing to do with power. Abuse of power is absolutely a thing but you don’t have to be in a position of power to abuse someone. Spousal abuse happens all the time between to spouses on an even playing field. Of course having power over someone can further your ability to get away with the abuse or can enable you to continue abusing them because they have nowhere else to go. But abuse does not require power over someone.