surety

Etymology

From Middle English surete, attested since the early 1300s in the sense "guarantee, promise, pledge, assurance", from Anglo-Norman seurté/Old French seurté with the same meaning (whence modern French sûreté), from Latin sēcūritās. Equivalent to sure + -ty. The senses "security, safety, stability" and "certainy" are attested since the late 1300s. "One who undertakes to pay if another does not" is from the early 1400s. Doublet of security.

noun

1. Certainty.
2. That which makes sure; that which confirms; ground of confidence or security.
3. (law) A promise to pay a sum of money in the event that another person fails to fulfill an obligation.
4. (law) One who undertakes to pay money or perform other acts in the event that his principal fails therein.
5. A substitute; a hostage.
6. Evidence; confirmation; warrant.