'unobtainable' originates from the prefix 'un-' meaning 'not' and the word 'obtain,' which comes from Latin 'obtinere,' where 'ob-' meant 'toward' and 'tenere' meant 'to hold.'

'obtinere' transformed into the Old French word 'obtenir,' and eventually became the modern English word 'obtain,' with 'un-' added to form 'unobtainable.'

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