I fail to see how you're regarding this as an offensive assault on Theism?
Most Atheists, including myself have simply stated it's not our place to define what God is.
There's hundreds, if not thousands of different definitions within Christianity alone. Every Christian has their own personal view of what God is. The only real common trait among all Christian definitions is that it's all powerful and created the universe.
But that doesn't go for non-christian interpretations of God. Some Gods are not all powerful, and many were not said to have created the universe.
So basically, my definition is: God is whatever the believer thinks it is.
For me, I think God does not exist. So therefore asking me to define something I don't think exists is senseless. That's like me asking you to define what a Martian looks like. There's a number of concepts from old movies, but in reality, martians have no definable characteristics at all, because they don't exist in reality.