Here is Henry Nelson Wieman’s minimalist definition of God. I first learned of it from Andrew James Brown who proposed to his congregation that it is the minimalist definition that everyone, despite their different maximalist conceptions of God could agree on.
Whatever else the word God may mean, it is a term used to designate that Something upon which human life is most dependent for its security, welfare and increasing abundance. That there is such a Something cannot be doubted. The mere fact that human life happens, and continues to happen, proves that this Something, however, unknown, does certainly exist.
Of course one can say that there are innumerable conditions which converge to sustain human life and that is doubtless a fact. But in that case either one of two things are true. Either the universe is a single individual organic unity, in which case it is the whole indivisible universe that has brought forth and now sustains human life; or else certain of these sustaining conditions are more critically, ultimately and constantly important for conditions are human welfare than are others. According to the first view God would be, or involve, the whole universe; according to the second he would be those most important conditions which, taken collectively, constitute the Something which must have supreme value for all human living. The word God, taken with its very minimum meaning, is the name for this Something of supreme value. God may be much more than this, but he is certainly this by definition. In this sense, with this minimum, God cannot be denied. His existence is absolutely certain. He is simply that which is supremely significant in all the universe for human living, however known or unknown he may be.
Of course this statement concerning God proves nothing about his character, except that he is the most beneficent object in the universe for human beings. He is certainly the object of supreme value. Nothing is implied by this definition concerning personality in God; but neither is personality denied. In fact, personality is by no means a clear and simple term. But two things are made certain: his existence and the supremacy of his value over all others, if we measure value in terms of human need.
References
Wieman, Henry Nelson. Religious Experience and Scientific Method. The Macmillan Company, 1926.