apostasy

The renunciation of a belief or set of beliefs.

The apparition of Lawyer Clippurse at the Hall occasioned much speculation in that portion of the world to which Waverley-Honour formed the centre: but the more judicious politicians of this microcosm augured yet worse consequences to Richard Waverley from a movement which shortly followed his apostasy.

The King of Navarre suddenly abandoned his party and went over to the Catholics. The explanation of his apostasy was as simple as it was base: Navarre had no confidence in the success of his cause, and he cared little in his heart for anything but women and vanity.

Specifically, the renunciation of one's religion or faith.