'rightfully-kept' originates from the combination of 'rightfully,' meaning 'in accordance with justice or law,' and 'kept,' the past participle of 'keep,' meaning 'to hold or retain.'

'rightfully-kept' evolved from the Old English word 'riht' meaning 'just' and 'cepan' meaning 'to seize or hold,' eventually forming the modern English compound adjective 'rightfully-kept.'

Initially, it meant 'justly held or retained,' and this meaning has largely remained the same in modern usage.