'unpredictable' originates from the prefix 'un-' meaning 'not' and the word 'predictable', which comes from Latin 'praedicere', where 'prae-' meant 'before' and 'dicere' meant 'to say'.

'praedicere' transformed into the Old French word 'predire', and eventually became the modern English word 'predict' with the addition of the prefix 'un-' to form 'unpredictable'.

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