1) Operation 2) Surgery 3) Surgical operation 4) Surgical procedure 5) Surgical process 
Removal of a circular piece ('button') of cranium by a trephine. ... Synonym: trepanation. ... (05 Mar 2000) ... 
(tref″ĭ-na´shәn) use of the trephine for creating an opening in the skull or in the sclera. dental trephination surgical creation of a fistula by puncturing the soft tissue and bone overlying the root apex to provide drainage. Called also apicostomy.
The surgical removal of a circular disc of bone or other tissue with a cylindrical saw.
Type: Term Pronunciation: tref′i-nā′shŭn Definitions: 1. Removal of a circular piece ('button') of cranium by a trephine. Synonyms: trepanation
[n] - a operation that removes a circular section of bone from the skull
noun a operation that removes a circular section of bone from the skull