'swiftly' originates from Old English, specifically the word 'swiftlice,' where 'swift' meant 'quick' and '-lice' was an adverbial suffix.

'swiftlice' transformed into the Middle English word 'swiftliche,' and eventually became the modern English word 'swiftly'.

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