'unsullied' originates from English, specifically formed from the prefix 'un-' and the past participle of 'sully', where 'un-' meant 'not' and 'sully' meant 'to soil'.

'sully' changed from the Old French word 'souiller' and entered Middle English as forms such as 'sullen' or 'sullien'; eventually English developed 'sully', and 'unsullied' was formed from 'un-' + 'sullied'.

Initially, it meant 'not soiled' (literally not dirtied), and over time it retained that sense while also extending to mean 'not tarnished in reputation' or 'morally unblemished'.