'commonly-separated' originates from the combination of 'common' and 'separate,' where 'common' meant 'usual' and 'separate' meant 'to divide or keep apart.'

'commonly-separated' evolved from the Middle English words 'commune' and 'separaten,' eventually becoming the modern English term 'commonly-separated.'

Initially, it meant 'frequently divided,' and this meaning has largely remained the same in modern usage.