The term "boundary marker" refers to a physical object that marks the limits of a certain area. Synonyms for this term include "boundary stone," which refers to a type of rock that is typically used to mark boundaries, and "boundary post," which is a wooden post that is used to demarcate a boundary. Other synonyms for "boundary marker" include "boundary monument," which refers to a significant structure that is placed at the boundary of a certain area, and "boundary fence," which is a type of barrier that is used to designate the limits of a certain property. Overall, these synonyms are all used to refer to the physical objects that are used to mark boundaries and demarcate different areas.