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countersink

[verb, noun koun-ter-singk; verb koun-ter-singk]
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verb (used with object), coun·ter·sank, coun·ter·sunk, coun·ter·sink·ing.
  1. to enlarge the upper part of (a cavity), especially by chamfering, to receive the cone-shaped head of a screw, bolt, etc.
  2. to cause (the head of a screw, bolt, etc.) to sink into a prepared depression so as to be flush with or below the surface.
noun
  1. a tool for countersinking a hole.
  2. a countersunk hole.

Origin of countersink

First recorded in 1810–20; counter- + sink
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for counter-sinking

countersink

verb -sinks, -sinking, -sank or -sunk (tr)
  1. to enlarge the upper part of (a hole) in timber, metal, etc, so that the head of a bolt or screw can be sunk below the surface
  2. to drive (a screw) or sink (a bolt) into such an enlarged hole
noun
  1. Also called: countersink bit a tool for countersinking
  2. a countersunk depression or hole
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012