'illness' originates from Old English, specifically the word 'illnes,' where 'ill' meant 'bad or evil' and '-ness' was a suffix forming nouns.

'illnes' changed from Old English word 'illnes' and eventually became the modern English word 'illness'.

Initially, it meant 'bad condition or evil state,' but over time it evolved into its current meaning of 'a state of being unwell or sick'.