fenestration /fen′əstrā″shən/ [L, fenestra, window] , 1. a surgical procedure in which an opening is created to gain access to the cavity within an organ or a bone. 2. an opening created surgically in a bone or organ of the body. 3. (in dentistry) a procedure to expose a root tip of a tooth to permit drainage of exudate. Also called window. −fenestrate, v.