Countersunk /(-s?nk`)/

Coun·ter·sunk

Countersunk

p. p. & a.
  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.