IPA: /ˈkɔɪnˌʊərər/
KK: /ˈkɔɪnˌʊrər/
A person or company that shares the financial risk of an insurance policy with another insurer.
The coinsurer agreed to cover part of the claim alongside the primary insurer.
Coinsurer → It is formed from "co-" (meaning together) and "insurer" (from the verb "insure", which comes from Latin "securare", meaning to make safe). The word "coinsurer" refers to a party that shares the responsibility of insurance with another party, thus working together in the insurance process.
Think of 'together' ('co-') working with someone to 'make safe' ('insurer') — that's what a coinsurer does.