To create a large hole by making a narrow groove outlining the shape of the hole and then removing the plug of material remaining by less expensive means
To perforate (the skull) with a trepan, so as to remove a portion of the bone, and thus relieve the brain from pressure or irritation; to perform an operation with the trepan
A crown-saw or cylindrical saw for perforating the skull, turned, when used, like a bit or gimlet
a drill for cutting circular holes around a center a surgical instrument used to remove sections of bone from the skull cut a hole with a trepan, as in surgery