If youlack that certain belief that god does exist you are not a theist - literally, you are atheist.
Interesting article...
By capella
Belief or without belief. Assertion or lack of assertion.
The words atheist and atheism are inaccurately defined in many dictionaries as someone who is a disbeliever/denier or has a doctrine that there is no God. Some dictionaries even include in their definitions phrases such as “immoral” or “someone with nothing to touch their inner being.”
My experience is that most atheists think an atheist is someone that is simply without any belief in gods.
This may not sound like a significant distinction to some, but it’s very important because sometimes atheism is portrayed as an assertion of a negative, which is a false argument. Sometimes atheism is also portrayed as a religion or doctrine which comes down to a matter of faith.
Although some dictionaries at least include the “without belief” phrase, the problem seems to be that dictionaries are about the common use of words, not whether the concept is necessarily valid.
For example:
“A nether world in which the dead continue to exist : (2) : the nether realm
of the devil and the demons in which the damned suffer everlasting punishment.”
(Merriam-Webster definition of “Hell”)
“The appearance of the sky when the sun starts to rise”
(Cambridge Dictionary definition of “sunrise”)
Although these definitions are how the words are probably most often used, some people might not agree that the definition of hell was factual and many people would agree that the sun doesn’t really “rise” (it appears to rise because of the turning of the earth).
Again, nit-picky? Yes, but the atheism definitions are often pulled out of dictionaries and paraded in discussions about the validity of atheism as if they are precise, valid, technical definitions.
Isn’t a lack of belief agnosticism?
Yes, but an agnostic is someone who asks a question about the existence of a particular god or gods and says that the answer is unknowable. The difference is that the atheist is not asking a question.
Does this imply the atheist thinks the matter is settled? No, it just means the atheist is not pursuing the question any more than the atheist would have a burning desire to know if Fred Flintstone exists.
http://www.goatstar.org/is-the-definition-of-an-atheist-really-someone-who-denies-the-existence-of-god/