Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

Source : WordNet®

credulity
     n : tendency to believe readily