n. [ A dim. of 1st trepan: cf. F. tréphine. ] (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. [ 1913 Webster ]

v. t. [ imp. & p. p. Trephined p. pr. & vb. n. Trephining. ] To perforate with a trephine; to trepan. [ 1913 Webster ]