countersink

noun

1. 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.
2. The cutter used to cut such a recess. (Also used, at less depth, for edge-breaking/deburring.)

   “Holonym: center drill (combined drill and countersink)”

verb

1. (transitive)To create such a conical recess.

   “to countersink a hole for a screw”

2. (ambitransitive)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.”