The Collaborative International Dictionary of English v.0.48:

Credible \Cred"i*ble\ (kr[e^]d"[i^]*b'l), a. [L. credibilis, fr.
   credere. See Creed.]
   Capable of being credited or believed; worthy of belief;
   entitled to confidence; trustworthy.
   [1913 Webster]

         Things are made credible either by the known condition
         and quality of the utterer or by the manifest
         likelihood of truth in themselves.       --Hooker.
   [1913 Webster]

         A very diligent and observing person, and likewise very
         sober and credible.                      --Dampier.
   [1913 Webster]

WordNet (r) 3.0 (2006):

credible
    adj 1: capable of being believed; "completely credible
           testimony"; "credible information" [syn: credible,
           believable] [ant: incredible, unbelievable]
    2: (a common but incorrect usage where `credulous' would be
       appropriate) credulous; "she was not the...credible fool he
       expected"
    3: appearing to merit belief or acceptance; "a credible witness"

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "credible":
   acknowledgment, admissible, asset, attention, authority,
   believable, cogent, colorable, conceivable, conclusive, confidence,
   convincing, credence, credit, creditable, determinative,
   distinction, faith, faithful, fame, fiduciary, glory, honor, just,
   justifiable, kudos, legitimate, likely, logical, notice, plausible,
   prestige, probable, rational, reasonable, recognition, reliable,
   reliance, renown, reputation, repute, sane, satisfactory,
   satisfying, sensible, solid, sound, straight, tenable, trust,
   trustworthy, trusty, unexceptionable, unimpeachable,
   unquestionable, valid, weight, well-argued, well-founded,
   well-grounded, wholesome, worthy of faith