Here's a breakdown:
* Countersinking: The process of enlarging the top of a hole at an angle to create a conical recess. This allows a screw head to sit flush with the surface.
* Counterbore: A cylindrical recess around a hole.
* Countersunk: The result of countersinking, a conical recess.
So, the term "counter" in "countersink" essentially means that the hole is being recessed or countersunk, creating a counterbore around the original hole. This recess allows the screw head to sit flush or below the surface, giving a smoother and more aesthetically pleasing finish.
Therefore, the term "counter" in "countersink" refers to the creation of a counterbore or a recessed area around the original hole.