(1) Holding established beliefs, especially in religion. (2) Conforming to established rules or traditions; conventional.
Example:
The O'Briens remain orthodox Catholics, faithfully observing the time-honored rituals of their church.
An orthodox religious belief or interpretation is one handed down by the founders or leaders of a church. When capitalized, as in Orthodox Judaism, Orthodox refers to branches within larger religious organizations that claim to honor the religion's original or traditional beliefs. The steadfast holding of established beliefs that is seen in religious orthodoxy is apparent also in other kinds of orthodox behavior. Orthodox medical treatment, for example, follows the established practices of mainstream medicine.