countersink
/ˈkaʊntəsɪŋk/verb
(past and past participle -sunk)with obj.
1- enlarge and bevel the rim of (a drilled hole) so that a screw, nail, or bolt can be inserted flush with the surface扩大（钻孔）的端口使其成埋头孔; 打埋头孔于。
1.1
- drive (a screw, nail, or bolt) into such a hole把（螺丝钉等）钻入埋头孔。