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