The Collaborative International Dictionary of English v.0.48:

guaranteed \guaranteed\ adj.
   1. secured by written agreement.

   Syn: bonded, secured, warranted.
        [WordNet 1.5]

   2. certified.
      [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Guarantee \Guar"an*tee`\, v. t. [imp. & p. p. guaranteed; p,
   pr. & vb. n. Guaranteeing.] [From Guarantee, n.]
   In law and common usage: to undertake or engage for the
   payment of (a debt) or the performance of (a duty) by another
   person; to undertake to secure (a possession, right, claim,
   etc.) to another against a specified contingency, or in all
   events; to give a guarantee concerning; to engage, assure, or
   secure as a thing that may be depended on; to warrant; as, to
   guarantee the execution of a treaty.
   [1913 Webster]

         The United States shall guarantee to every State in
         this Union a republican form of government.
                                                  --Constitution
                                                  of the U. S.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

certified \certified\ adj.
   1. endorsed authoritatively as having met certain
      requirements; guranteed; as, certified milk; certified
      mail; a certified check. Opposite of uncertified.
      [Narrower terms: certificated, credentialed, documented;
      guaranteed] See also certifiable.
      [WordNet 1.5]

   2. legally insane according to clinical criteria.

   Syn: certifiable.
        [WordNet 1.5 +PJC]

   3. holding appropriate documentation and officially on record
      as qualified to perform a specified function or practice a
      specified skill.

   Syn: qualified.
        [WordNet 1.5]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "guaranteed":
   affianced, ascertained, assured, attested, betrothed, bound,
   certain, certified, committed, compromised, contracted, covered,
   decided, dependable, determinate, determined, engaged, ensured,
   established, fail-safe, firm, fixed, harmless, in the bag, insured,
   intended, invulnerable, made sure, nailed down, obligated, on ice,
   open-and-shut, pledged, plighted, promised, proved, reliable,
   riskless, secure, secured, set, settled, sound, stable, stated,
   steady, sure, sworn, tested, tried, trustworthy, undangerous,
   underwritten, unhazardous, unperilous, unprecarious, unrisky,
   warranted, warranteed