It's not "popular, it's historically .
I would like you to tell me what one thing all of these definitions have in common.
Definition of orthodoxy
1. of, relating to, or conforming to the approved form of any doctrine, philosophy, ideology, etc.
2. of, relating to, or conforming to beliefs, attitudes, or modes of conduct that are generally approved.
3. customary or conventional, as a means or method; established.
4. sound or correct in opinion or doctrine, especially theological or religious doctrine.
5. conforming to the Christian faith as represented in the creeds of the early church.
6. (initial capital letter) of, relating to, or designating the Eastern Church, especially the Greek Orthodox Church.
7. (initial capital letter) of, relating to, or characteristic of Orthodox Jews or Orthodox Judaism.