verb (used with object), coun·ter·bored, coun·ter·bor·ing.
Examples from the Web for counterbore
The jaw end is counterbored out with a 45-degree counterbore to form a bearing for the forward end of the micrometer screw.Measuring Tools|Unknown
If taken off at all it must be pulled, for the dowel-pins, key and counterbore are close fits.Steam Turbines|Hubert E. Collins
That it may always do this and yet leave sufficient clearance, the counterbore has been devised.Farm Engines and How to Run Them|James H. Stephenson
For counterboring small holes or for facing the metal around their ends, the form of counterbore shown in Fig. 1746 is employed.
For enlarging a hole for a certain distance the counterbore is employed.