When talking about paying for something over time, the word "instalments" is a common term used. However, there are a few other synonyms to use instead. One option is "payments", as this is a general term that refers to any money paid towards a debt or purchase. Another synonym is "installments", which is just a variation of the same word. Another option is "dues", which implies that there is a specific amount owed and due at certain times. Lastly, "deferred payments" can be used if the payments are being pushed back to a later date. Overall, these synonyms all capture the idea of paying for something over time.