'患病' is a verb meaning 'to fall ill' or 'to become sick.' It combines two characters: 患 (huàn), which means 'to suffer from' or 'to be afflicted with,' and 病 (bìng), meaning 'illness' or 'disease.' Together, they form a compound verb emphasizing the onset or presence of illness — not just feeling unwell temporarily, but having contracted a diagnosable condition. It's commonly used in formal, medical, or written contexts, such as health reports, news articles, or doctor-patient communication.

The word typically appears in subject–verb constructions, often followed by a specific illness (e.g., 患病肺炎 'contract pneumonia') or used without an object when the illness is understood from context. Unlike colloquial expressions like '感冒了' (caught a cold), '患病' carries a more serious or clinical tone and is rarely used for minor ailments like headaches or fatigue.