A cold or a virus is an example of an illness.
There is serious illness in her family.
She was terrified by his illness, and yet that was just what she needed.
How has his whole illness gone?
No particulars are known of his last illness, but it seems likely that death came upon him rather suddenly at,last.
Proposing to seek his fortune abroad, he went on foot to Nantes, but was there prostrated by an illness so severe that all thoughts of emigration were perforce abandoned.