What does "surety" mean?

Additional senses

1. 2.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. Milton.
2. 3.Security against loss or damage; security for payment, or for the performance of some act. There remains unpaid A hundred thousand more; in surety of the which One part of Aquitaine is bound to us. Shak.
3. 4.(Law) One who is bound with and for another who is primarily liable, and who is called the principal; one who engages to answer for another's appearance in court, or for his payment of a debt, or for performance of some act; a bondsman; a bail. He that is surety for a stranger shall smart for it. Prov. xi.
4. 5.5. Hence, a substitute; a hostage. Cowper.
5. 6.Evidence; confirmation; warrant. [Obs.] She called the saints to surety, That she would never put it from her finger, Unless she gave it to yourself. Shak.
6. 7.To act as surety for. [Obs.] Shak.