noun (n)

• an inclination to do something(noun.feeling)

  Synonym:
  leaning, tendency
  

  source: wordnet30
• a natural inclination(noun.cognition)

  Synonym:
  leaning, proclivity
  

  source: wordnet30
• a disposition to behave in a certain way(noun.attribute)

  Example:
  The propensity of disease to spread.
  

  Synonym:
  aptness
  

  source: wordnet30
• The quality or state of being propense; natural inclination; disposition to do good or evil; bias; bent; tendency.(noun)

  source: webster1913