The Collaborative International Dictionary of English v.0.48:

Certification \Cer`ti*fi*ca"tion\, n. [L. certificatio: cf. F.
   certification.]
   The act of certifying.
   [1913 Webster]

WordNet (r) 3.0 (2006):

certification
    n 1: the act of certifying or bestowing a franchise on [syn:
         certification, enfranchisement] [ant:
         disenfranchisement]
    2: confirmation that some fact or statement is true through the
       use of documentary evidence [syn: documentation,
       certification, corroboration]
    3: a document attesting to the truth of certain stated facts
       [syn: certificate, certification, credential,
       credentials]
    4: validating the authenticity of something or someone [syn:
       authentication, certification]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "certification":
   John Hancock, OK, acceptance, affidavit, affirmance, affirmation,
   approbation, approval, ascertainment, assurance, attestation,
   authentication, authority, authorization, backing, backing up,
   bearing out, bill of health, bolstering, buttressing, certificate,
   certificate of proficiency, check, checking, circumstantiation,
   clearance, collation, confirmation, corroboration,
   corroboratory evidence, countenance, countersignature, credential,
   deposition, determination, diploma, documentation, empowerment,
   enabling, endorsement, enfranchisement, ensuring, entitlement,
   establishment, fiat, fortification, go-ahead, green light,
   imprimatur, navicert, nod, notarization, notarized statement, note,
   okay, permission, proof, proving, proving out, ratification,
   reassurance, reassurement, reinforcement, rubber stamp, sanction,
   seal, sheepskin, sigil, signature, signet, stamp,
   stamp of approval, statement under oath, strengthening,
   subscription, substantiation, support, supporting evidence,
   swearing, sworn statement, sworn testimony, testamur, testimonial,
   testimony, the nod, ticket, undergirding, validation, verification,
   visa, vise, voucher, vouching, warrant, warranty, witness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CERTIFICATION or CERTIFICATE OF ASSISE. A term used in the old English law,
applicable to a writ granted for the reexamination or retrial of a matter
passed by assise before justices. F. N. B. 181 3 Bl. Com. 389. The summary
motion for a new trial has entirely superseded the use of this writ, which
was one of the means devised by the judges to prevent a resort to the remedy
by attaint for a wrong verdict.