countersink
Concise Oxford English Dictionary © 2008 Oxford University Press:
countersink/ˈkaʊntəsɪŋk/
▶verb (past and past part. countersunk) enlarge and bevel the rim of (a drilled hole) so that a screw or bolt can be inserted flush with the surface.
■ drive (a screw or bolt) into such a hole.
'countersink' also found in these Oxford entries:

