—v.t. 1. to enlarge the upper part of (a cavity), esp. by chamfering, to receive the cone-shaped head of a screw, bolt, etc.
2. to cause (the head of a screw, bolt, etc.) to sink into a prepared depression so as to be flush with or below the surface.
—n. 1. a tool for countersinking a hole.
2. a countersunk hole.