This is the 363rd most frequent Chinese word.
疾病
"疾病" means "disease" or "illness."
In this context, '疾病' (illness) is used to describe a psychological condition.
他由于长期的压力发展出了心理疾病。
He developed a mental illness due to prolonged stress.
Here, '疾病' refers to illnesses in a general context, which can include various health conditions.
这些疾病可以通过预防措施来避免。
These illnesses can be avoided through preventive measures.
In this sentence, '疾病' specifies a particular disease that is the subject of medical research.