'unaccompanied' originates from Middle English, specifically the word 'acompanyen,' where 'a-' meant 'to' and 'compaign' meant 'companion.'

'acompanyen' transformed into the modern English word 'accompany,' and eventually 'unaccompanied' was formed by adding the prefix 'un-' to indicate the absence of a companion.

Initially, it meant 'without a companion,' and this meaning has largely remained the same in modern usage.