cosignatory
noun [ C ]
uk/ˌkəʊˈsɪɡnətəri/ us/ˌkəʊˈsɪɡnətɔri/ (also co-signatory)one of two or more people, countries or organizations who sign an official agreement or document:
He is a cosignatory to a letter, published in the Financial Times.
Canada is a co-signatory of the North American Free Trade Agreement.
a person or organization that signs a document already signed by another person, agreeing to pay that person’s debt if they fail to do so:
British students in the US need a local co-signatory to apply for a loan.
one of two or more people or organizations who take equal responsibility for a financial arrangement:
When one of the co-signatories dies, all of the assets in the joint bank account will continue to be available to their partner.
As a co-signatory to the mortgage, she is considered a joint investor in the fund.