IPA: /njuːməˈθɔːræks/
KK: /njuməˈθɔræks/
A medical condition where air or gas collects in the space around the lungs, which can happen due to injury or disease, and may cause the lung to collapse.
The doctor diagnosed him with a pneumothorax after he complained of sudden chest pain.
Pneumothorax is formed from "pneumo-" (from Greek "pneuma", meaning air or breath) and "thorax" (from Greek "thorax", meaning chest). The term describes the presence of air in the chest cavity, which can lead to lung collapse.
Think of 'air' ('pneumo-') in the 'chest' ('thorax') — that's what pneumothorax refers to, the condition of having air in the chest.