apostasy

/əˈpɑstəsi/

Other forms: apostasies

If your lifelong Republican-voting grandfather suddenly decides to register as a Democrat, some of his conservative friends may consider his change in politics to be apostasy, or rejecting what has been a strong belief and adopting a new one.

When you abandon a set of beliefs, especially when they're religious beliefs, you can be accused of apostasy, which in some countries is actually illegal. It's taken seriously by many churches, since the rejection of a church's ideas can be seen as a criticism of the entire organization. Over time, the meaning of apostasy has grown to include non-religious examples, like your grandfather's political switch.

Definitions of apostasy

1. noun

   the state of having rejected your religious beliefs or your political party or a cause (often in favor of opposing beliefs or causes)
   synonyms: defection, renunciation

   type of:

   rejection

   the state of being rejected
2. noun

   the act of abandoning a party or cause
   synonyms: tergiversation

   type of:

   abandonment, desertion, forsaking

   the act of giving something up