'unjustifiably' originates from the English word 'unjustifiable', which is derived from the prefix 'un-' meaning 'not', and 'justifiable', which comes from the Latin 'justificare', where 'justus' meant 'just' and 'facere' meant 'to make'.

'unjustifiable' changed from the Old French word 'justifiable' and eventually became the modern English word 'unjustifiable'.

Initially, it meant 'not able to be justified', and this meaning has largely remained the same in modern usage.