'annuity' originates from Latin, specifically the word 'annuitas', where 'annus' meant 'year'.

'annuity' changed from Medieval Latin 'annuitas' (also attested in Old French/Anglo-Norman forms) and entered Middle English as 'annuite' or 'annuitie', eventually becoming the modern English word 'annuity'.

Initially, it meant 'a yearly payment' and over time it evolved into the modern financial sense of a contract or product providing regular (often lifelong) payments; the core idea of 'yearly payment' has been retained but usage expanded into insurance/finance contexts.