'lightly' originates from Old English, specifically the word 'lēohtlīce,' where 'lēoht' meant 'light' and '-līce' was an adverbial suffix.

'lēohtlīce' transformed into the Middle English word 'lightliche,' and eventually became the modern English word 'lightly'.

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