Coun″ter‐sink′ (koun″tẽr‐sĭṉk′; 277), v. t. [imp. & p. p.Countersunk (–sŭṉk′); p. pr. & vb. n.Countersinking.] 1. To chamfer or form a depression around the top of (a hole in wood, metal, etc.) for the reception of the head of a screw or bolt below the surface, either wholly or in part; as, to countersink a hole for a screw.
2. To cause to sink even with or below the surface; as, to countersink a screw or bolt into woodwork.