'goodness' originates from Old English, specifically the word 'gōdnes', where 'gōd' meant 'good' and the suffix '-ness' formed a noun meaning 'state or quality'.

'goodness' changed from Old English 'gōdnes' to Middle English 'goodnes' and eventually became the modern English word 'goodness'.

Initially it meant 'the state or quality of being good'; over time the noun sense has remained, while the word also developed use as an interjection (a mild exclamation or euphemism).