a. - Sound in opinion or doctrine, especially in religious doctrine; hence, holding the Christian faith; believing the doctrines taught in the Scriptures; -- opposed to heretical and heterodox; as, an orthodox Christian.
a. - According or congruous with the doctrines of Scripture, the creed of a church, the decree of a council, or the like; as, an orthodox opinion, book, etc.
a. - Approved; conventional.