I just asked a question titled "What is the difference between a Heretic and a Schismatic" , and when I was selecting the tags, I noticed that I could use the tags "Heretic" and "Schism".
I believe heresy is a better tag than heretic, as the former suggests a group of people while the latter suggests a single person.
"Schism" likewise suggests the belief of a group of people, whereas "schismatic" suggests the belief of one person.
Actually both tags already existed so I'm not sure why you chose to tag your question with the variant you say here (and I agree) is not as optimal. I have retagged your question and the other two on the site that used heretic with heresy. I also merged the plural version into the main one. As long as no questions pop up using the wrong tags in a couple days the now empty tags will be removed automatically.
I don't really see the need for synonyms at this point as only a few oddball questions had the variant tags. If this proves to be an ongoing point of confusion after the existing tags no longer auto-complete then we can certainly make synonyms.
