The word "back" has several synonyms that can be used in different contexts. One of the synonyms is "rear," which refers to the back part of something. For instance, the rear of a car or the rear of a building. Another synonym is "spine," which is commonly used in the anatomy context to refer to the back bone. Additionally, "behind" can be used to refer to the backside of something, such as a chair or a person. "Return" can also be used as a synonym for "back," especially in the context of going back or coming back from somewhere. Other synonyms for "back" include "posterior," "dorsal," and "reverse".