noun (n)

• the state of having rejected your religious beliefs or your political party or a cause (often in favor of opposing beliefs or causes)(noun.state)

  Synonym:
  defection, renunciation
  

  source: wordnet30
• the act of abandoning a party for cause(noun.act)

  Synonym:
  tergiversation
  

  source: wordnet30
• An abandonment of what one has voluntarily professed; a total desertion of departure from one's faith, principles, or party; esp., the renunciation of a religious faith; as, Julian's apostasy from Christianity.(noun)

  source: webster1913