'untroubled' originates from Middle English, specifically the word 'troublen,' where 'un-' meant 'not' and 'troublen' meant 'to disturb or agitate.'

'troublen' transformed into the modern English word 'trouble,' and with the prefix 'un-' it became 'untroubled.'

Initially, it meant 'not disturbed or agitated,' and this meaning has largely remained the same in modern usage.