Believer

Noun

 * 1) A person who believes; especially regarding religion.

Adjectives for Believer
devout; ardent; passionate; true; firm; conscientious; tremendous; frantic; lifelong; unquestioning; consummate; fervent; enthusiastic; rapt.

Thesaurus
accepter, catechumen, churchgoer, churchite, churchman, communicant, convert, cultist, daily communicant, devotee, devotionalist, disciple, fanatic, fideist, follower, good Christian, ist, neophyte, pietist, proselyte, receiver, religioner, religionist, religious believer, saint, the assured, the believing, the faithful, theist, true believer, truster, votary, zealot

Antonyms

 * infidel
 * unbeliever