(1):

(imp. & p. p.) of Countersink

(2):

(p. p. & a.) Sunk into a chamfer; as, a countersunk bolt.

(3):

(p. p. & a.) Chamfered at the top; - said of a hole.

(4):

(p. p. & a.) Beveled on the lower side, so as to fit a chamfered countersink; as, a countersunk nailhead.