Actually the greek word it stems from is 'atheos', not 'a-theism'. The prefix 'a' means 'without', the 'theos' meaning God.
So by definition, the word atheism does not make it a "lack of religion". Atheists can be religious (some Buddhists spring to mind), but what the word means is literally "without God". A person "without God". A religion, of course, requires more than just that. A religion requires a specific dogma to follow, and usually a metaphysical explanation for the state of things in the universe (and the universe itself).
That is why atheism (and theism) is not a religion.
So by definition, the word atheism does not make it a "lack of religion". Atheists can be religious (some Buddhists spring to mind), but what the word means is literally "without God". A person "without God". A religion, of course, requires more than just that. A religion requires a specific dogma to follow, and usually a metaphysical explanation for the state of things in the universe (and the universe itself).
That is why atheism (and theism) is not a religion.
