Relying on Webster's for a theological term is like going to Hardee's for a elaborate romantic dinner
Good analogy. However, our Christian religions are considered heretical in other countries. The definition meeans different things to different people. To me, it is someone who espouses Christianity or purports to live a good life, but who demonstrates the exact opposite. I guess I fall into that category sometimes so what am I to say anything? Christianity was considered heretical during the time of Jesus. Other religions were considered heretical by the Catholic Church.
"To me, it is someone who espouses Christianity or purports to live a good life, but who demonstrates the exact opposite."
That's hypocrisy, not heresy. Heresy is espousing a false doctrine, I don't know why Webster's would say Christian doctrine or mainly RC doctrine, I suppose that could be accurate but I'd say the concept could apply to any religion.
Suppose I say Buddah never really acheived nirvana, he just died and got buried. I think to a Buddhist that would make me a heretic, if I was myself a Buddhist. I think that is part of it, you can't be a heretic unless you are a member of the relgion you are giving "false" information about.
And, not to be confused with blasphemy.