'indistinguishable' originates from Latin, specifically the word 'indistinguibilis,' where 'in-' meant 'not' and 'distinguere' meant 'to separate or distinguish.'

'indistinguibilis' transformed into the Old French word 'indistinguible,' and eventually became the modern English word 'indistinguishable' through Middle English.

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