'undecidable' originates from the prefix 'un-' meaning 'not' and the word 'decidable' from Latin 'decidere', where 'de-' meant 'off' and 'caedere' meant 'to cut'.

'decidere' transformed into the Old French word 'decider', and eventually became the modern English word 'decide', with 'undecidable' forming by adding the prefix 'un-'.

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