'reassure' originates from Old French, specifically the word 'rassurer,' where 're-' meant 'again' and 'assurer' meant 'to assure.'

'rassurer' transformed into the Middle English word 'reassuren,' and eventually became the modern English word 'reassure.'

Initially, it meant 'to assure again,' but over time it evolved into its current meaning of 'to remove doubts and fears.'