The Collaborative International Dictionary of English v.0.48:

Approbation \Ap`pro*ba"tion\, n. [L. approbatio: cf. F.
   approbation. See Approve to prove.]
   1. Proof; attestation. [Obs.] --Shak.
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   2. The act of approving; an assenting to the propriety of a
      thing with some degree of pleasure or satisfaction;
      approval; sanction; commendation.
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            Many . . . joined in a loud hum of approbation.
                                                  --Macaulay.
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            The silent approbation of one's own breast.
                                                  --Melmoth.
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            Animals . . . love approbation or praise. --Darwin.
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   3. Probation or novitiate. [Obs.]
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            This day my sister should the cloister enter,
            And there receive her approbation.    --Shak.
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   Syn: Approval; liking; sanction; consent; concurrence.

   Usage: Approbation, Approval. Approbation and approval
          have the same general meaning, assenting to or
          declaring as good, sanction, commendation; but
          approbation is stronger and more positive. "We may be
          anxious for the approbation of our friends; but we
          should be still more anxious for the approval of our
          own consciences." "He who is desirous to obtain
          universal approbation will learn a good lesson from
          the fable of the old man and his ass." "The work has
          been examined by several excellent judges, who have
          expressed their unqualified approval of its plan and
          execution."
          [1913 Webster]

WordNet (r) 3.0 (2006):

approbation
    n 1: official approval
    2: official recognition or approval [ant: condemnation,
       disapprobation]

Moby Thesaurus II by Grady Ward, 1.0:

100 Moby Thesaurus words for "approbation":
   John Hancock, OK, acceptance, accord, account, acquiescence,
   adherence, admiration, adoration, affirmance, affirmation,
   affirmative, affirmative voice, agreement, apotheosis,
   appreciation, approval, assent, authentication, authorization, awe,
   aye, benediction, blessing, breathless adoration, certification,
   commendation, compliance, confirmation, connivance, consent,
   consideration, countenance, countersignature, courtesy, credit,
   deference, deification, duty, eagerness, endorsement, esteem,
   estimation, exaggerated respect, favor, favorable vote, go-ahead,
   goodwill, great respect, green light, hero worship, high regard,
   homage, honor, idolatry, idolization, imprimatur, liking, nod,
   notarization, okay, permission, pleasure, prestige, promptitude,
   promptness, ratification, readiness, regard, respect, reverence,
   reverential regard, rubber stamp, sanction, satisfaction, seal,
   seal of approval, sigil, signature, signet, stamp,
   stamp of approval, submission, subscription, the nod,
   ungrudgingness, unloathness, unreluctance, validation, veneration,
   visa, vise, voice, vote, warrant, willingness, worship, worth, yea,
   yea vote