What are the dimensions?
An abrader is a tool that was used to create a rough surface on the edge of a flint preform, so as to make it possible to remove exact flakes in the creation of a spear point. Normally, an adrader is held in the hand. It gets scarred up similar to the marks on your object. It is possible that it was used like a workbench to sharpen bone awls, or prepare platforms on the flint, like I described above.
Good luck finding out!