Crossword Genius

Shaft borer (6)

Ross

I believe the answer is:

trepan

(Other definitions for trepan that I've seen before include "Make perforation in person's skull" , "Surgical instrument used to remove sections of bone from the skull" , "old saw" , "Surgically create a hole in the skull" , "cut through bone" .)

I've seen this clue in The Sunday Times.
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