'impassable' originates from the Latin word 'impassibilis', where 'im-' meant 'not' and 'passibilis' meant 'able to be passed'.

'impassibilis' transformed into the Old French word 'impassable', and eventually became the modern English word 'impassable'.

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