Synonyms for Surety (same or very similar meaning)
WordNet sense 1 (property that your creditor can claim in case you default on your obligation):
securityWordNet sense 2 (a prisoner who is held by one party to insure that another party will meet specified terms):
hostageWordNet sense 3 (one who provides a warrant or guarantee to another):
guarantor, warranter, warrantorFrom the ODE community, based on WordNetadd/edit