her·e·tic, noun, one who dissents from an accepted belief or doctrine
No, no. If we’re going to sling around religious terminology, we’d better consult the experts:
“Heresy is the obstinate post-baptismal denial of some truth which must be believed with divine and Catholic faith, or it is likewise an obstinate doubt concerning the same …”
— The Catechism of the Catholic Church (CCC 2089)
We use the word pretty casually in Christian circles when
someone says something a little off the spiritually-beaten track, but mostly we mean it frivolously.