Agnostic (noun) अनीश्वरवादी/ संशयवादी - a person who claims that they cannot have true knowledge about the existence of God (but does not deny that God might exist).
e.g. Although he was raised a Catholic, he was an agnostic for most of his adult life.
Atheist (noun) नास्तिक - a person who does not believe in God or gods.
e.g. As an atheist, I do not accept this religious argument.