əˈpɒstəsi dɪˈfɛkʃən the act of renouncing; sacrificing or giving up or surrendering (a possession or right or title or privilege etc.) rejecting or disowning or disclaiming as invalid Congressional repudiation of the treaty that the President had negotiated an act (spoken or written) declaring that something is surrendered or disowned the state of having rejected your religious beliefs for your political party or a cause (often in favor of opposing beliefs or causes)