a cylindrical recess, typically machined around a hole to admit a screw so that it sits flush with a surface.
To create such a conical recess.
To cause to sink even with or below the surface.
A surgical instrument with a cylindrical blade used to remove a circular section of tissue, f.e. bone or cornea; a trepan.
To use a trephine during surgery.
To perforate with a trephine.