A person who believes in the truth or existence of something
she was a believer in the Christian religion
A person who does not believe in a particular thing, especially one who has no religious faith
A member of a Russian Orthodox group which refused to accept the liturgical reforms of the patriarch Nikon (1605–81)
I was an absolute non-believer in spiritualism
(In various Protestant denominations, originally and especially in the Baptist Church) baptism administered as an adult or adolescent, when a person is considered capable of fully understanding the sacrament; opposed to infant-baptism.