'unsustainable' originates from the prefix 'un-' meaning 'not' and the word 'sustainable', which comes from the Latin 'sustinere', where 'sub-' meant 'under' and 'tenere' meant 'to hold'.

'sustinere' transformed into the Old French word 'soustenir', and eventually became the modern English word 'sustain'. The prefix 'un-' was added to form 'unsustainable'.

Initially, 'sustain' meant 'to hold up or support', but over time, 'sustainable' evolved to mean 'able to be maintained', and 'unsustainable' as 'not able to be maintained'.