guarantor
noun [ C ]
FINANCE uk/ˌɡærənˈtɔːr/ us/-ˈtɔːr/a person or organization that promises to pay back a loan if the person or organization that originally borrowed the money does not:
guarantor for/on sth Some providers lend young people more if their parents agree to be guarantor for the loan.
The private investor acted as guarantor to £160 million of the company's bank borrowings.