Source : Webster's Revised Unabridged Dictionary (1913)

Credibleness \Cred"i*ble*ness\, n.
   The quality or state of being credible; worthiness of belief;
   credibility. [R.] --Boyle.

Source : WordNet®

credibleness
     n : the quality of being believable or trustworthy [syn: {credibility},
          {believability}] [ant: {incredibility}]