'improbability' originates from Latin, specifically the word 'improbabilis,' where 'im-' meant 'not' and 'probabilis' meant 'provable or credible.'

'improbabilis' transformed into the French word 'improbabilité,' and eventually became the modern English word 'improbability' through Middle English.

Initially, it meant 'not credible or unlikely,' and this meaning has largely remained the same in modern usage.