'sum' originates from Latin, specifically the word 'summa', where 'summa' meant 'total, highest'.

'sum' changed from Old French 'somme' and Medieval Latin 'summa' and eventually became the modern English word 'sum' through Middle English.

Initially it meant 'total' or 'highest amount', and over time it evolved to include the verb sense 'to add together' as well as the noun sense 'total'.