countersink

From counter- + sink.

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countersink (plural countersinks)

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.

   Coordinate term: counterbore (cylindrical)

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

   Synonym: countersinker

   Hypernyms: cutter, cutting tool

   Holonym: center drill (combined drill and countersink)

   Coordinate terms: counterbore (cylindrical); drill, drill bit; reamer; endmill

countersink (third-person singular simple present countersinks, present participle countersinking, simple past countersank or countersunk, past participle countersunk)

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

   • 2010, Larry Pardey, Details of Classic Boat Construction, pages 7-30:

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

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