The Million Dollar Question

[Confused Ape]

Well many of God’s attributes are explicitly mentioned in scripture itself.
As for the rebuking of heretical teachings by the early church, this seems to only substantiate by claim that Christians have had a very definite definition of God for a long time.

The Christian faction which won interpreted scripture to back up their claim that God is a Trinity. It took the members of this faction several centuries to finalise the 'orthodox' opinion, though.

They used that definition to correct or rebuke anyone who created their own false definition. We still use the writings of the early church fathers today because the theology has been so consistent.

That's the theology of the winning faction. It's not surprising that their theology has been fairly consistent.

There's no Trinity in Judaism. God was always chatting to people in the Old Testament. You'd think he'd have mentioned he's a Trinity to somebody, especially Moses.

The Eastern Orthodox Church may be a bit offended that you seemed to forget that they even exist.

The Eastern Orthodox Church still has the Trinity etc. along with an interesting history..

In the 11th century what was recognised as the Great Schism took place between Rome and Constantinople, which led to separation between the Church of the West, the Roman Catholic Church, and the Eastern Byzantine Churches, now the Orthodox. There were doctrinal issues like the filioque clause and the authority of the Roman Pope involved in the split, but these were greatly exacerbated by political factors of both Church and state, and by cultural and linguistic differences between Latins and Greeks. Prior to 1054, the Eastern and Western halves of the Church had frequently been in conflict, particularly during the periods of Eastern iconoclasm and the Photian schism.[154]

The final breach is often considered to have arisen after the capture and sacking of Constantinople by the Fourth Crusade in 1204; the final break with Rome occurred circa 1450.

The Roman Catholics were dealing with all the upheaval of the Crusading Decline in the 13th and 14th centuries. It's likely they were disinclined to take on the Eastern Church's empire as well. After all, it would have been a different kettle of fish to wiping out sects like the Cathars.

And then -

In 1453, the Byzantine Empire fell to the Ottoman Empire. By this time Egypt had been under Muslim control for some seven centuries, but Orthodoxy was very strong in Russia which had recently acquired an autocephalous status; and thus Moscow called itself the Third Rome, as the cultural heir of Constantinople.

Under Ottoman rule, the Greek Orthodox Church acquired substantial power as an autonomous millet. The ecumenical patriarch was the religious and administrative ruler of the entire "Greek Orthodox nation" (Ottoman administrative unit), which encompassed all the Orthodox subjects of the Empire.

It's likely that they were disinclined to take on Russia and the Ottoman Empire too. It might have been a different story, though, if the Eastern Church had adopted a Gnostic theology and taught that the God of the Old Testament was an evil Demiurge.

Non-Trinitarians are actually a great minority and regarded by most as non-Christian churches. Interestingly enough, I was just talking to a couple Jehovah’s Witnesses on my front lawn the other day and to say that they are Christians is simply inaccurate. They have borrowed much of our terminology but that’s about it.

Many of the non-Trinitarian denominations won't regard you as a real Christian either. Some Protestants don't regard the Roman Catholics as real Christians. Then there's the Eastern Orthodox Church again.

The Orthodox understand themselves to be the One Holy Catholic and Apostolic Church; the true Church established by Jesus Christ and placed into the care of the apostles. As almost all other Christian groups are in indirect schism with the Orthodox Church, mostly as a result of the Great Schism with the Roman Catholic Church at the turn of the second Christian millennium (prior to the additional schisms of the Protestant Reformation), these other groups are viewed as being Christian, but who in varying degrees lack full theological orthodoxy and orthopraxy.

As such, all groups outside of the Orthodox Church are not seen as being members of the Church proper, but rather separated brethren who have failed to retain the fullness of the Christian faith and theology, as was given to the apostles by Jesus Christ. These deviations from orthodoxy have traditionally been called heresy, but due to the term's immediately pejorative connotations, some prefer the more technical designation of the term heterodoxy.

How do you like being regarded as a heretic by millions of other Christians?

That was not the original question though was it? The original question was to define the term god, not to prove any god exists.

Existence is very relevant to the definition, though. Believers think their deities exist but there's no concrete proof that any of them really do exist.