Atheist (n) : A person who believes that God does not exist
Definition from Merriam-Webster (http://www.merriam-webster.com/dictionary/atheist)
From What You Pawn I Will Redeem by Sherman Alexie (in the part of 6a.m)
“I believe you’ll take my money and get drunk on it.”
“Then why are you giving it to me?”
“There ain’t no such thing as a atheist cop.”
Officer William gave 30 dollars to Jackson Jackson, even though he knew that Jackson would spend the money on drinking, because he is not a person who believes that God does not exist.