The Collaborative International Dictionary of English v.0.48:

Propensity \Pro*pen"si*ty\, n.; pl. Propensities.
   The quality or state of being propense; natural inclination;
   disposition to do good or evil; bias; bent; tendency. "A
   propensity to utter blasphemy." --Macaulay.
   [1913 Webster]

   Syn: Disposition; bias; inclination; proclivity; proneness;
        bent; tendency.
        [1913 Webster]