1) Operate on with a trephine 2) Surgical instrument 3) Surgical saw 4) Surgical instrument 5) To perforate with a trephine 6) Trepan 1) Trepan 
A trephine (n; from Latin trypan, meaning to bore){dubious|date=May 2014|reason=Etymology dubious. See for example http://www.etymonline.com/index.php?allowed_in_frame=0&search=trephine&searchmode=none. Trypan btw is a-the Greek infinitive.} is a surgical instrument with a cylindrical blade. It can be of one of several dimensions and designs depen...
• (n.) 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. • (v. t.) To perforate with a trephine; to trepan.
A surgical tool used to cut out circular pieces of bone or other tissue.
(trә-fīn´) (trә-fēn´) a saw for removing a disk of bone, chiefly from the skull. an instrument for removing a circular area of cornea. to remove with this instrument.
Type: Term Pronunciation: trē-fīn′, -fēn′ Definitions: 1. To remove a disc of bone or other tissue by means of a trephine. Synonyms: perforator
A trephine is a surgeon's cylindrical saw with a guiding centre pin used for removing part of the bone of the skull. The trephine took over from the earlier trepan. Trephines are used for removing bullets or bone fragments loged in the skull and pressing upon the brain, or for the removal of blood clots or tumours etc in the head. Ancient skulls ha...
[v] - operate on with a trephine
noun a surgical instrument used to remove sections of bone from the skull
A cylindrical saw