The Collaborative International Dictionary of English v.0.48:

Surety \Sure"ty\, n.; pl. Sureties. [OE. seurte, OF.
   se["u]rt['e], F. s[^u]ret['e]. See Sure, Security.]
   1. The state of being sure; certainty; security.
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            Know of a surety, that thy seed shall be a stranger
            in a land that is not theirs.         --Gen. xv. 13.
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            For the more surety they looked round about. --Sir
                                                  P. Sidney.
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   2. That which makes sure; that which confirms; ground of
      confidence or security.
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            [We] our happy state
            Hold, as you yours, while our obedience holds;
            On other surety none.                 --Milton.
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   3. Security against loss or damage; security for payment, or
      for the performance of some act.
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            There remains unpaid
            A hundred thousand more; in surety of the which
            One part of Aquitaine is bound to us. --Shak.
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   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.
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            He that is surety for a stranger shall smart for it.
                                                  --Prov. xi.
                                                  15.
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   5. Hence, a substitute; a hostage. --Cowper.
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   6. Evidence; confirmation; warrant. [Obs.]
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            She called the saints to surety,
            That she would never put it from her finger,
            Unless she gave it to yourself.       --Shak.
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The Collaborative International Dictionary of English v.0.48:

Surety \Sure"ty\, v. t.
   To act as surety for. [Obs.] --Shak.
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Easton's 1897 Bible Dictionary:

Surety
one who becomes responsible for another. Christ is the surety of
the better covenant (Heb. 7:22). In him we have the assurance
that all its provisions will be fully and faithfully carried
out. Solomon warns against incautiously becoming security for
another (Prov. 6:1-5; 11:15; 17:18; 20:16).

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "surety":
   absolute certainty, absoluteness, acceptation, acception,
   acquiescence, angel, arrogance, assurance, assuredness, backer,
   bail, bailsman, belief, bond, bondsman, certain knowledge,
   certainness, certainty, certitude, clear sailing, cocksureness,
   confidence, confidentness, conviction, courage, credence, credit,
   credulity, dead certainty, definiteness, dependence, determinacy,
   determinateness, earnest, earnest money, escrow, faith, gage,
   godfather, godparent, guarantee, guarantor, guaranty, handsel,
   harmlessness, hock, hope, hostage, hubris, immunity, indemnity,
   ineluctability, inerrability, inerrancy, inevitability,
   infallibilism, infallibility, insurance, insurer, invulnerability,
   mainpernor, mainprise, mortgagor, necessity, nonambiguity,
   noncontingency, overconfidence, oversureness, overweening,
   overweeningness, patron, pawn, pignus, pledge, poise, pomposity,
   positiveness, predestination, predetermination, pride, probatum,
   protection, proved fact, reception, recognizance, reliance,
   reliance on, replevin, replevy, risklessness, safeguard, safeness,
   safety, security, self-assurance, self-confidence, self-importance,
   self-reliance, settled belief, sponsor, stock, stocks and bonds,
   store, subjective certainty, sureness, suspension of disbelief,
   tie, token payment, trust, truth, unambiguity, undertaking,
   underwriter, unequivocalness, univocity, unmistakableness,
   vadimonium, vadium, warrant, warrantor, warranty