'brotherly' originates from Old English, specifically the word 'brōðorlic,' where 'brōðor' meant 'brother' and '-lic' meant 'like or pertaining to.'

'brōðorlic' transformed into the Middle English word 'brotherly,' and eventually became the modern English word 'brotherly.'

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