a slightly novel argument for God's existence.

Consider principle

(A) Any non-arbitrary definition is indicative of a real thing.

Argument for (A): How else could a definition be non-arbitrary if it weren’t for the real thing that it’s tracking? Therefore, (A).

Now consider

(1) The definition of ‘God’ is not arbitrary.

Argument for (1): Consider your definition of ‘God’. While you’re grouping various predicates together (perhaps omnipotence, omnibenevolence?) ask yourself the following question: are the predicates I’m picking to include in my definition of God such that I’m picking them willy-nilly or not? If not, then you don’t think that the definition of God is arbitrary. Hence, (1).

Well, so what? This: If the definition of God is not arbitrary, and any non-arbitrary definition is indicative of a real thing, then God is a real thing. And every time we have a real thing (and not just a real nature), that thing exists. Hence,

(2) God exists.