trephine

v. (Medicine) perform surgery with a small circular saw for cutting circular discs of bone

n. small circular saw for cutting circular discs of bone (Medicine)

A trephine is a surgical instrument with a cylindrical blade. It can be of one of several dimensions and designs depending on what it is going to be used for. They may be specially designed for obtaining a cylindrically shaped core of bone that can be used for tests, cutting holes in bones (i.e. the skull) or for cutting out a round piece of the cornea for eye surgery.
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Trephine /tre·phine/ 1. a crown saw for removing a disk of bone, chiefly from the skull. 2. an instrument for removing a circular area of cornea. 3. [more]Trephine - Community and Resources

Noun
1. a surgical instrument used to remove sections of bone from the skull
(synonym) trepan
(hypernym) surgical instrument
Verb
1. operate on with a trephine
(hypernym) operate on, operate
(derivation) trephination

(v. t.)
To perforate with a trephine; to trepan.
  

(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.