'unextendable' originates from the prefix 'un-' meaning 'not' and the word 'extendable', which comes from Latin 'extendere', where 'ex-' meant 'out' and 'tendere' meant 'to stretch'.

'extendere' transformed into the Old French word 'estendre', and eventually became the modern English word 'extend'. The prefix 'un-' was added to form 'unextendable'.

Initially, 'extendere' meant 'to stretch out', but over time, 'extendable' evolved to mean 'capable of being extended', and 'unextendable' as 'not capable of being extended'.