'cleanly' originates from Old English, specifically the word 'clænlīce,' where 'clæne' meant 'clean' and '-līce' was an adverbial suffix.

'clænlīce' transformed into the Middle English word 'clenliche,' and eventually became the modern English word 'cleanly'.

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