'brightly' originates from Old English, specifically the word 'beorhtlice,' where 'beorht' meant 'bright' and '-lice' was an adverbial suffix.

'beorhtlice' transformed into the Middle English word 'brightliche,' and eventually became the modern English word 'brightly'.

Initially, it meant 'in a bright manner,' and this meaning has largely remained the same in modern usage.