Illness (noun)

1. 1. a state of poor health.
2. 2. a disease or medical condition.

Origin:

Middle english (in the sense "evil, wickedness"): from old english gilness, from gil "disease", of germanic origin; related to ill.

Examples:

1. She was off work for a month with an illness.
2. He had a serious illness.
3. The illness was caused by a virus.
4. The illness spread rapidly through the office.
5. His illness was diagnosed as pneumonia.