'unendurable' originates from the prefix 'un-' meaning 'not' and the word 'endurable', which comes from Latin 'endurare', meaning 'to make hard'.

'endurare' transformed into the Old French word 'endurer', and eventually became the modern English word 'endure'.

Initially, it meant 'to make hard or strong', but over time it evolved into its current meaning of 'to withstand or tolerate'.