surgical instrument: a cylindrical sharp or sawtooth-edged surgical instrument, used especially to cut a hole in the skull. It is also used in corneal grafting to remove an opaque disk from a cornea so that it can be replaced with a clear disk.
transitive verb (past and past participletre·phined, present participletre·phin·ing, 3rd person present singulartre·phines)
Definition:
remove circle of bone or tissue: to remove a circular section from a bone, especially the skull, or from corneal tissue with a trephine
[Early 17th century. < Latin tres fines "three ends," partly after trepan1]
