'sourness' originates from Old English, specifically the word 'sūrnes,' where 'sūr' meant 'sour' and '-nes' was a suffix indicating a state or quality.

'sūrnes' transformed into the Middle English word 'sournes,' and eventually became the modern English word 'sourness'.

Initially, it meant 'the state of being sour,' and this meaning has largely remained the same in modern usage.