pneumothorax n 1: abnormal presence of air in the pleural cavity resulting in the collapse of the lung; may be spontaneous (due to injury to the chest) or induced (as a treatment for tuberculosis)
Pneumothorax \Pneu`mo*tho"rax\, n. [Gr. ? air + E. thorax.] (Med.) A condition in which air or other gas is present in the cavity of the chest; -- called also {pneumatothorax}. [1913 Webster]