'certainty' originates from Old French, specifically the word 'certeinté', where 'cert-' meant 'sure' and '-té' was a suffix forming nouns.

'certeinté' transformed into the Middle English word 'certeynte', and eventually became the modern English word 'certainty'.

Initially, it meant 'surety or assurance', but over time it evolved into its current meaning of 'the state of being certain'.