trepan trepan /trɪˈpæn/

noun

1. A drill for cutting circular holes around a center  ( trepan )
   a drill for cutting circular holes around a center
    The surgeon studied the ancient technique of trepanation, using a trepan to make holes in the skull.
   The surgeon studied the ancient technique of trepanation, using a trepan to make holes in the skull.
   
   
2. A surgical instrument used to remove sections of bone from the skull  ( trepan , trephine )
   a surgical instrument used to remove sections of bone from the skull
   
   

verb

1. Cut a hole with a trepan, as in surgery  ( trepan )
   cut a hole with a trepan, as in surgery