security against loss or damage or for the fulfillment of an obligation, the payment of a debt, etc.; a pledge, guaranty, or bond.

a person who has made himself or herself responsible for another, as a sponsor, godparent, or bondsman.

the state or quality of being sure.

certainty.

something that makes sure; ground of confidence or safety.

a person who is legally responsible for the debt, default, or delinquency of another.

assurance, esp. self-assurance.

noun

assurance , assuredness , certainty , certitude , confidence , conviction , positiveness , guaranty , warrant , warranty , backer , guarantor , underwriter , bail , bondsman , corroboration , guarantee , hostage , pledge , ratification , security , sponsor , substitute , sureness