'inexcusable' originates from Latin, specifically the word 'inexcusabilis,' where 'in-' meant 'not' and 'excusabilis' meant 'excusable.'

'inexcusabilis' transformed into the Old French word 'inexcusable,' and eventually became the modern English word 'inexcusable.'

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