The Collaborative International Dictionary of English v.0.48:

Credibility \Cred`i*bil"i*ty\ (kr[e^]d`[i^]*b[i^]l"[i^]*t[y^]),
   n. [Cf. F. cr['e]dibilit['e].]
   The quality of being credible; credibleness; as, the
   credibility of facts; the credibility of witnesses.
   [1913 Webster]

WordNet (r) 3.0 (2006):

credibility
    n 1: the quality of being believable or trustworthy [syn:
         credibility, credibleness, believability] [ant:
         incredibility, incredibleness]