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