surety

noun6

1. •
   That which makes sure; that which confirms; ground of confidence or security.

   • [We] our happy state Hold, as you yours, while our obedience holds; On other surety none. — 1667
2. •
   One who undertakes to pay money or perform other acts in the event that his principal fails therein.

   • He that is surety for a stranger shall smart for it. — 1611
3. •
   A promise to pay a sum of money in the event that another person fails to fulfill an obligation.

   • There remains unpaid A hundred thousand more; in surety of the which One part of Aquitaine is bound to us. — 1595
4. •
   Certainty.

   • Know of a surety, that thy seed shall be a stranger in a land that is not theirs. — 1611
5. •
   Evidence; confirmation; warrant.

   • She called the saints to surety, That she would never put it from her finger, Unless she gave it to yourself. — 1604
6. •
   A substitute; a hostage.