Source : Webster's Revised Unabridged Dictionary (1913)

Believer \Be*liev"er\, n.
   1. One who believes; one who is persuaded of the truth or
      reality of some doctrine, person, or thing.

   2. (Theol.) One who gives credit to the truth of the
      Scriptures, as a revelation from God; a Christian; -- in a
      more restricted sense, one who receives Christ as his
      Savior, and accepts the way of salvation unfolded in the
      gospel.

            Thou didst open the Kingdom of Heaven to all
            believers.                            --Book of Com.
                                                  Prayer.

   3. (Eccl. Hist.) One who was admitted to all the rights of
      divine worship and instructed in all the mysteries of the
      Christian religion, in distinction from a catechumen, or
      one yet under instruction.

Source : WordNet®

believer
     n 1: a supporter who accepts something as true [syn: {truster}]
     2: a person who has religious faith [syn: {worshiper}, {worshipper}]