'impenetrable' originates from Latin, specifically the word 'impenetrabilis,' where 'in-' meant 'not' and 'penetrabilis' meant 'able to be pierced.'

'impenetrabilis' transformed into the Old French word 'impenetrable,' and eventually became the modern English word 'impenetrable' through Middle English.

Initially, it meant 'not able to be pierced,' but over time it evolved into its current meanings of 'impossible to pass through' and 'impossible to understand.'