Atheism is a lack of belief in ...what?
Without gods, there is no atheism. Until a baby knows what is God he or she is not atheist
This truly is getting off-topic, but I'll answer since its likely to be googled by someone in the future.
Atheism describes
without gods. As a label, it exists only
after the assertion by others that god(s) exist(s) (theists).
If there were no majority asserting that god(s) exist(s), there would be no need to refer to those that do not accept this assertion. If belief in unicorns became a majority belief, I would probably consider myself a a-unicornist. Belief in ghosts is widespread, and if aghostist where as easy to say as atheist, I'd likely use it. As it is, I happily refer to myself as a non-believer in ghosts. This doesn't imply that ghosts must first exist, nor does it imply that I was born with a belief in ghosts to begin with.
The
word atheist is simply a word. A label. The meaning can be whatever you wish it to be. You can define it however you like. Those who self-define as atheists, however, utilize the definition "a lack of belief in god(s)."
New born babies are non-believers in gods. They lack a belief in gods among many, many other things. They are atheists.
I agree, that without the term "theist" the term "atheist" would not exist. There would be no need for it. Without believers in gods, we would not need to refer to those that lack belief in gods. There may be a civilization on another planet in another galaxy that has a belief in something that neither of us have ever conceived of. Neither of us was born with a belief in whatever this concept is, but this same civilization may have a label for those who are non-believers. We must, out of necessity, fall under that label even though we do not know what it is or what it translates to.