ism <- the belief in
the <- a god
A <- a lack of
Atheism means a lack of belief in god. It does not mean you assert that there is no god, it does not mean you're sure that god doesn't exist. All an atheist person is, is someone who lacks a positive belief in a god.
Agnosticism is a bs answer. If you don't assert that there is a god, you are atheist, regardless of weather or not you want to be associated with that. If you think it's unknowable, therefore you withhold judgement, you are an atheist, because you lack positive belief in a god.
About time we cleared this up. You can be a so called 'strong atheist' where you have a positive belief that there is no god, and that is still atheism. But that does not represent all of what the word means.