The Collaborative International Dictionary of English v.0.48:

Credulity \Cre*du"li*ty\ (kr?-d?"l?-t?), n. [L. credulitas, fr.
   credulus: cf. F. cr['e]dulit['e]. See Credulous.]
   Readiness of belief; a disposition to believe on slight
   evidence.
   [1913 Webster]

         That implict credulity is the mark of a feeble mind
         will not be disputed.                    --Sir W.
                                                  Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

credulity
    n 1: tendency to believe readily