1. a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects: the Christian religion; the Buddhist religion.
3. the body of persons adhering to a particular set of beliefs and practices: a world council of religions.
4. the life or state of a monk, nun, etc.: to enter religion.
5. the practice of religious beliefs; ritual observance of faith.
Nope didnt see disbelief in there at all. The key aspect to a religion is that its a collective belief system. That is why Buddhism is a listed as a religion, because its a set of beliefs generally believed by a collective.
But honestly their could be a Atheist religion. That is if a collective adhered to a belief system. But then that would make them fake atheists. So in reality it is impossible for a atheism to be a religion since it would stop being atheism when it became a religion.
But the people claiming that atheism is a religion do so to against a secular government. Its a tactic that asserts that atheism/secularism is a religion so that they can install their own religion (Christianity) into the Government despite the Constitution. So they figured that by listing atheism/secularism they will be one step closer to making everyone good little Christians. And its to the gallows for atheism/secularism.
Of course they will deny all of that severely, but then why must they do what they are doing in such a underhanded dishonest fashion?