The antonyms for the word "mis-believer" are believer, faithful, follower, devout, orthodox, and traditionalist. A believer is someone who trusts and has faith in something or someone. A faithful person is loyal and steadfast in their beliefs, practices, and commitments. A follower is someone who adheres to the teachings and guidance of a particular leader or ideology. A devout individual is devoted to their religious or spiritual beliefs, often showing great reverence and piety. Orthodox people adhere strictly to traditional beliefs, practices, and customs, while traditionalists are staunch supporters of time-honored customs and values. In contrast to a "mis-believer," all these terms describe individuals who have strong convictions and beliefs.