Force habit refers to a behavior or action that has become so ingrained in a person that it is difficult to change. There are a few different synonyms that can be used to describe this concept. A common term is "compulsion," which refers to an irresistible urge to do something. "Rote," on the other hand, refers to a behavior that has become automatic and is performed without much thought. "Routine" is another related term that connotes a regular pattern of behavior or activity. Finally, "inertia" can be used to describe the tendency of a person or system to continue operating in a certain way, even when change is needed.