The Collaborative International Dictionary of English v.0.48:
Thoracotomy \Tho`ra*cot"o*my\, n. [Gr. ?, ?, thorax + ? to cut.] (Surg.) The operation of opening the pleural cavity by incision. [1913 Webster]WordNet (r) 3.0 (2006):
thoracotomy n 1: surgical incision into the chest walls opening up the pleural cavity