<p><strong>Noun:</strong></p><ul><li>A small circular saw with a center pin mounted on a strong hollow metal shaft to which is attached a transverse handle.</li><li>Used in surgery to remove circular disks of bone from the skull.</li></ul><p><strong>Verb:</strong></p><ul><li>To operate upon with a trephine.</li><li>Trephined, trephining.</li></ul>