What's the Word When Some One Rejects the Faith?

A lot of times we are making conclusions about people standing with god and we don't even have a relation ship with them to discern correctly. I just think that it takes humility and patience and holy spirit driven wisdom to be able to come to those kinds of conclusions. And then again, my other brain, i's like, but can you know though? Cause, i mean, john says, who have been born of god will not continue in sin. Even paulin hebrews talks about those who are, what's the word when some one rejects the faith? It starts with a a.