'sickly' originates from Old English, specifically the word 'seoclic,' where 'seoc' meant 'sick' and '-lic' was a suffix meaning 'like' or 'having the qualities of.'

'seoclic' transformed into the Middle English word 'sikly,' and eventually became the modern English word 'sickly.'

Initially, it meant 'having the qualities of being sick,' and this meaning has largely remained the same in modern usage.