David Mo
Philosopher
The reason why it can be important is because Theist's often try to redirect the burden of proof onto the Atheist. "You cant prove god doesn't exist!" as if this wins some kind of argument. When you explain to them what you mean by Atheist in order to show them they actually have the burden of proof they tend to say something like "oh, then your just an Agnostic" which tends to imply that you (me) just haven't figured it out yet but that they have - like they are ahead of the curve and you just need to catch up.
It's all semantics and word play but it can be annoying. It is possible to be an Agnostic Theist or an Agnostic Atheist. You can be an Atheist for different reasons, including being convinced a god doesn't exist. Theists are often Agnostic because they rely on their faith. They can't be sure there is a God and admit they cannot prove it, but they are convinced nonetheless.
Even if I accept your definition for Atheist (which I don't, even your dictionary paste doesn't entirely support it), it still leaves the theist with everything to still to do to be able to rationalize their belief in a creator of the universe.
The dictionary you mention was etymological. The English dictionaries I have consulted either use the meaning I use or mention the two possible meanings without mention the combination "Atheist agnostic", etc.. There are exceptions but few. Here is the Encyclopedia Britannica, which is a reference text:
Atheism, in general, the critique and denial of metaphysical beliefs in God or spiritual beings. As such, it is usually distinguished from theism, which affirms the reality of the divine and often seeks to demonstrate its existence. Atheism is also distinguished from agnosticism, which leaves open the question whether there is a god or not, professing to find the questions unanswered or unanswerable. (https://www.britannica.com/topic/atheism )
Of course the theist is setting you a semantic trap when he says that if you are actually an agnostic you are "out of the curve". I don't know what that means, nor why being an agnostic leaves you behind, but you are lost if you accept the starting point that there is a "real" or "authentic" meaning of the word "atheist" or "agnostic". There they'll nail you with quotes like the Encyclopaedia Britannica or Huxley to show that you don't know what you're talking about.
Names are flatus vocis, i.e. air in the mouth. What really matters are things. Don't stick to the name and go to the idea, to the meaning. You are someone who doesn't believe in God. You shouldn't present any proof. It is the task for the believer. They will try to show off with names. Don't let them. Go to the idea like a bull-dog.
