a surgical instrument used to remove sections of bone from the skull
<noun.artifact> [ verb ]
operate on with a trephine
<verb.body>
Trephine \Tre*phine"\ (?; 277), n. [A dim. of 1st trepan: cf. F. tr['e]phine.] (Surg.) An instrument for trepanning, being an improvement on the trepan. It is a circular or cylindrical saw, with a handle like that of a gimlet, and a little sharp perforator called the center pin.
Trephine \Tre*phine"\, v. t. [imp. & p. p. {Trephined}; p. pr. & vb. n. {Trephining}.] To perforate with a trephine; to trepan.