'unquenchable' originates from Middle English, specifically the word 'quenchen,' where 'un-' meant 'not' and 'quenchen' meant 'to put out or extinguish.'

'quenchen' transformed into the modern English word 'quench,' and with the prefix 'un-' it became 'unquenchable.'

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