'brightness' originates from Old English, specifically the word 'beorhtnes,' where 'beorht' meant 'bright' and '-nes' was a suffix indicating a state or quality.

'beorhtnes' changed from Old English to Middle English as 'brihtnes,' and eventually became the modern English word 'brightness'.

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