Religion .

a person who does not accept a particular faith, esp. Christianity.

(in Christian use) an unbeliever, esp. a Muslim.

(in Muslim use) a person who does not accept the Islamic faith; kaffir.

a person who has no religious faith; unbeliever.

(loosely) a person who disbelieves or doubts a particular theory, belief, creed, etc.; skeptic.

not accepting a particular faith, esp. Christianity or Islam; heathen.

without religious faith.

due to or manifesting unbelief

infidel ideas.

rejecting the Christian religion while accepting no other; not believing in the Bible or any Christian divine revelation.

Also, infidelic

noun

agnostic , atheist , gentile , heathen , heretic , nonworshiper , pagan , unbeliever , free-thinker , skeptic