trephine, n. [A dim. of 1st trepan: cf. F. tréphine.].
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. [1913 Webster]
trephine, v. t.
To perforate with a trephine; to trepan. [1913 Webster]