Select the option which is the most appropriate one word substitution for the given group of words.

One who holds established opinions

orthodox

The most appropriate option which is the one-word substitution for the given group of words "one who holds established opinions" is orthodox.

• Missionary is a person sent on a religious mission.
• Monotheist is a person who believes that there is only one God.
• Atheist is a person who disbelieves or lacks belief in the existence of God.

The word orthodox is the most appropriate because it specifically refers to someone who holds traditional or generally accepted beliefs. The other words do not have the same connotation of being someone who adheres to established opinions.