1) Atheist 2) Disbeliever 3) Infidel 4) Irreligionist 5) Nonbeliever 1) Disbeliever 2) Nonbeliever 3) Nonreligious person 
• (n.) One who does not believe; an incredulous person; a doubter; a skeptic. • (n.) A disbeliever; especially, one who does not believe that the Bible is a divine revelation, and holds that Christ was neither a divine nor a supernatural person; an infidel; a freethinker.
a person who does not believe. · a person who does not accept any, or some particular, religious belief.