illness、sickness、disease与complaint这些名词均有“疾病”之意。
illness : 不具体指，而是泛指一切疾病，强调生病的时间或状语，语体较sickness正式一些。
- He died at home after a long illness.
久病之后他在家里死去。 - She had five days off work due to illness.
她因病请了5天假。
sickness : 较口语化，可与illness换用，但还可表示“恶心、呕吐”。
- There's a lot of sickness around this winter.
今年冬天患病的人很多。 - Drinking unclean water can cause diarrhoea and sickness.
饮用不洁净的水会导致腹泻和呕吐。
disease : 指具体的疾病，且通常较严重，发病时间也较长。引申指人或社会的恶疾、弊病。
- a contagious/infectious disease
传染病 - a common/rare/incurable/fatal disease
常见病／罕见疾病／绝症／致命疾病 - They reported a sudden outbreak of the disease in the south of the country.
他们报告说该国南部地区突然爆发了这种疾病。 - The first symptom of the disease is a very high temperature.
这种病的最初症状是高烧。 - She has caught/contracted (= begun to have) a lung disease/disease of the lungs.
她患上了肺病。 - Starvation and disease have killed thousands of refugees.
饥饿和疾病夺去了数千名难民的生命。
- The real disease affecting the country is inflation.
影响该国的真正恶疾是通货膨胀。
complaint : 现代英语中，既可指症状，也可指疾病。
- a heart/stomach complaint
心脏／胃病
