'Countersunk' definitions:

Definition of 'Countersunk'

From: GCIDE

Countersink \Coun"ter*sink`\ (koun"t[~e]r*s[i^][ng]k`; 277), v. t. [imp. & p. p. Countersunk (-s[u^][ng]k`); 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. [1913 Webster]
2. To cause to sink even with or below the surface; as, to countersink a screw or bolt into woodwork. [1913 Webster]

From: GCIDE

Countersunk \Coun"ter*sunk`\ (-s?nk`), p. p. & a. from Countersink.
1. Chamfered at the top; -- said of a hole. [1913 Webster]
2. Sunk into a chamfer; as, a countersunk bolt. [1913 Webster]
3. Beveled on the lower side, so as to fit a chamfered countersink; as, a countersunk nailhead. [1913 Webster]