The antonym of atheist is theist. An atheist is someone who does not believe that god(s) exist, or that there is no reason to believe that they exist. A theist is someone who believes that god(s) exist and that there is sufficient reason to believe that they exist.
Atheism.
There is no real opposition, but atheism could probably be considered "opposite"
atheism
Atheism is a noun.
Atheism is the belief that there is no god.
There are no prophets of atheism.
George H. Smith has written: 'Atheism, Ayn Rand, and other heresies' -- subject(s): Atheism, Philosophy, Religion and state 'The Wealth of Nations Part 1' 'Why Atheism?' -- subject(s): atheism 'Atheism' -- subject(s): atheism, Atheism, Controversial literature, Christianity
Atheism is not a religion. [S] [V] [o] Here you are, a complete sentence with atheism.
Atheism is the lack of belief in God.
Atheism was never established, as it is not a religion.
"Atheism is not a religion."
Atheism is by definition not a religion.