Empyema
An empyema (from Greek ἐμπύημα, “abscess”) is a collection or gathering of pus within a naturally existing anatomical cavity. For example, pleural empyema is empyema of the pleural cavity. It must be differentiated from an abscess, which is a collection of pus in a newly formed cavity.
Wikipedia
Empyema (noun)
A collection of pus within a naturally existing anatomical cavity (as opposed to an abscess, which occurs in a newly formed cavity).
Emphysema (noun)
An abnormal accumulation of air or other gas in tissues, most commonly the lungs.
Emphysema (noun)
Pulmonary emphysema, a chronic lung disease, one type of chronic obstructive pulmonary disease.
Wiktionary