1. noun /ˈdiːˌkɒnvɜːt,ˌdiːkənˈvɜːt/
An apostate.
2. verb /ˈdiːˌkɒnvɜːt,ˌdiːkənˈvɜːt/
a) To undergo a deconversion from a religion, faith or belief or to induce (someone) to reject a particular religion, faith, or belief.
She has deconverted from Christianity, Islam, Judaism, etc.
They tried to deconvert him.
Wikipedia foundation.