1.NounA surgical instrument with a cylindrical blade used to remove a circular section of tissue, such as bone or cornea; a trepan.
"They removed a core of bone as well as took a bone marrow aspirate from my right hip using a trephine to exclude me having blood cancer, causing a blood- and serum-stained shirt, a whopping hematoma and a great deal of mental anguish and physical pain in the process!"