IPA: /ɪnˈstɔːlmənt/
KK: /ɪnˈstɔlmənt/
A part of a payment that is made at regular intervals until a debt is fully paid off.
I will pay for the car in three installments over the next few months.
Installment → It is formed from "in-" (meaning in or into) and "stalla" (from Latin "stare", meaning to stand). The word refers to a payment that stands in or is made in parts over time.
Think of making payments 'in' ('in-') parts that 'stand' ('stare') over time — that's what an installment means.