In belief, meaning is not the point
Definitions are a funny thing. When you don't examine the matter too much, they just seem like vague conventions that people use so they can have a proper language. When you start delving in philosophical issues, you start to realize that definitions, with their loaded meanings and vague implications, filter how we see the world. Eventually you come to realize that definitions, as they circumscribe everything we know about existents, are an integral part of one's worldview.
Defining concepts rationally and with precision is not the first step to a solid framework, it's the only step.
The word "god" doesn't escape that - in fact, because it subsumes existents that are nothing but fictional characters at best, it is a perfect example of that. It's easier to subsume things that actually exist, since you have an objective standard you can refer to. But fictional characters derived from old mythological ways of thinking, which have no relation to modern values ? That's a problem. Even elves in Lord of the Rings are easier to define than "god", since Tolkien provided us with plenty of fictional instances of elves. In the Bible, there's only one god with any prominence.
So where do we go from here ? Well, we can look at how believers define their gods. You have the fire-and-brimstone fundies and cultists, who portray God as a powerful, violent, father-like being, the "Bruce Almighty"-like believers, who portray God as an impotent, loving, "bigger brother" type, the New Agers, who relate to religious concepts as metaphors for self-empowerment or connection with a higher reality, and then you've got the synchronicity fans, who see God as little more than a giant mathematical contrivance sending us "messages" by timing the passage of cars or making one person meet another.
That's personality, but what is the ontological nature of this god ? That is the one point they all agree on, it has no ontological nature. It is non-material, non-natural, non-definable. Its actions and thoughts, its purpose in creating or influencing human beings, remain totally unknowable. The meaning of "god" is, and remains, totally nil.
But this is not a surprise. Any attempt to give meaning to "god" would be to limit it, and "god" is precisely an imaginary construct that must remain without limits in order to provide the "transcendent creator" needed by believers to make sense of order. Defining is a limitation, a circumscription, therefore "god" cannot be defined or be made meaningful.
Remember that religion is a meme complex, and it must be able to change if it is to adapt to social circumstances. And belief cannot change if it remains pinned to a definition. This is where the concept of belief-doctrine independence comes in. If you can reframe your reading of the Bible strongly enough, you can ignore all the parts that contradict your specific sect or personal beliefs.
But here's the rub - how do you do this with a definition ? Even if somehow there was no conflict between limiting "god" and the "transcendent creator" belief, it would mean that the religion could no longer adapt. If you've got "god" pinned down to one specific conception, with a specific set of epistemic, moral and political beliefs attached to it, then the religion would die out the second social circumstances change and make that set of beliefs undesirable.
So "god", like other religious terms which do not correspond to any existents, is a symbol. A symbol is a mental shortcut meant to evoke the "right" emotional response at the push of a linguistic button - like a name (like "Jesus Christ"), a code-word (like "family values"), a graphic (like the cross), a flag, a sports team logo.
Terms like "god", which are based on fantasy, can only be integrated within the inter-subjective context which creates them. If you tell a Christian, "God created the universe", the Christian will understand you because he's been trained to understand these symbols in a specific way, with the associated emotional responses. If you look at "God created the universe", there's no way to make any sense of that. The universe cannot be "created", since creation requires pre-existing matter, and no being can exist if the universe does not exist.
So the last, and perhaps most important, question is : how can atheists make sense of the same sentence "God created the universe" ? If "God" is meaningless, then how can atheists talk about it outside of the inter-subjective religious framework ?
Well, we can only talk about things that relate to reality. And we can relate such a sentence to reality, even if we have to do it piecemeal. In fact, I think that's how atheists do it already. Even though "God created the universe" makes no sense in and of itself, we can still reduce it to the following :
cause of – the universe
cause of – all natural events
temporally prior to – the universe
We can make sense of "cause of", "temporally prior to", "the universe" and "all natural events", and use them in arguments that prove the non-existence of God, even if we don't believe that the sum total of the property has any meaning. Of course, if "god" meant anything we would not need these mental gymnastics at all, and I don't blame any atheist who rejects them in favour of a more practical "God is a fantasy and we don't need to debate this" approach.