countersink

A conical recess, typically machined at the mouth of a hole to admit a screw (with a matching taper) so that the screw sits flush with a surface.

The cutter used to cut such a recess. (Also used, at less depth, for edge-breaking/deburring.)

Holonym: center drill (combined drill and countersink)

To create such a conical recess.

to countersink a hole for a screw

To cause to sink even with or below the surface.

to countersink a screw or bolt into woodwork

I countersank into the locust just enough to make the nailhead flush.