We're defining it differently in PS
Maybe you should start a glossary.
I remember a few discussions that circled around definitions, at the end it turned out that PS just uses a different definition for a common word.
Say you would use "globe" in PS. People assume you are referring to something round, but due to your own definition it is rectangular.
How can you wonder why people misunderstand?
So, not only in this case but in general, if you use a common human languange, better use the same common definitions. To derive from this I neither find any original, nor is it any user friendly.
Why not simply call it heathendom, disbelief or faithlessness?