Okay so what I understand about the word giant is that it all started when the greeks had the mythological creature called the gigantes, who the french knew about. England interacted with the norse countries and got the idea of jotun. When William the conquerer conquered England, he changed the word jotun into the same word that he had for gigantes since they were similar concepts (big things that fought against the gods), and over time the two concepts and the word evolved into a singular thing known as a "Giant". Since england was christian they discarded the parts about giants fighting against god (as nothing but demons can fight against god) and came up with their own giant myth of brutes who threw rocks around, based off of a combination of the gigantes and the jotunn. Then people like saxo grammaticus thought that giants must be real because they explained old roman architecture. And then because wales is close to England they picked up the idea of a giant from england and wroght the Four Branches of the Mabinogi which codified giants as we know them today. (I may be wrong about this though)
But my question is, Where do nephilim fit into all of this? Unlike other big mythological creatures I see nephlim described as giants fairly often (ie, nephlim = giant while ogree=/=giant) when did that start? My gut instinct is that people described nephilim as giant due to their size, and people got confused and thought that they were giants. But I would also believe that when the english were coming up with thier idea of giants they were combining the jotunn, the gigantes, AND the nephilim. Is calling nephlim giants a new thing? Or is that the british already beleived that nephlim were big brutes who threw rocks around, and the new french word was originally used to describe nephlim? Is my premise wrong?
Your intricate question - and your understanding of the topic - is grounded on a diffusion model: "it all started with the Greeks"; the Welsh "picked up the idea ... from England", etc. This connecting of dots and the assumption that underpins your question is problematic.
Folklorists have long understood that stories diffuse and can jump cultural and linguistic boundaries, but beliefs in supernatural beings usually don't (unless there is a significant movement of people). As stories diffuse, they are adapted to indigenous belief systems and the local supernatural beings believed to exist.
Belief in an archaic time when there were giants is actually widespread. These entities are usually relegated to an ancient time when they were held responsible for various natural and human-made things (for example, the Giant's Causeway in Northern Ireland). In the same way, people generally believed that giants were long gone and one was not likely to encounter one. The Celtic fringe - including Ireland, Scotland, Wales and Cornwall - all had indigenous stories about various monuments that were made by an ancient race of giants. This almost certainly did not diffuse from the English. There was also a widespread belief in giants in Scandinavia and among Germanics-speaking people in general, so it is no surprise to find similar entities in Old Norse literature and in Anglo-Saxon texts (and then in the folklore of the more recent descendants of these people). That said, the belief in giants did not diffuse from one to the other. But the shared cultural bedrock allowed for similar stories to diffuse throughout Europe, and for these stories to be modified as needed to suit local circumstance.
Since an ancient race of giants is also attested to in Classical Greek and Roman mythology, it is easy to postulate that there was an Indo European belief in giants, but whether the European beliefs in these creatures represents a diffusion with the language some three or four millennia ago or there was simply a larger "stew" of traditions is difficult to say.
At the same time, it is clear from the Old Testament and various other Middle Eastern texts that there was also a tradition of an ancient race of giants in those areas where Indo-European languages were not commonly spoken. It is part of this indigenous tradition that likely inspired the authors of the Hebrew religious texts to document a belief in the Nephilim. Because of the widespread traditions describing giants in the Middle East, it is easy to suspect (but difficult to prove), that these cultures also had this sort of tradition for a long while.
We do not need a post-classical period of diffusion to explain the widespread giant traditions. It seems that they had been well-established in the indigenous folk traditions for a long time.
For sources, an early authority on defining what can diffuse and what generally does not was Carl Wilhelm von Sydow (1878-1952); see his Selected Papers on Folklore, Laurits Bødker, editor (Copenhagen: Rosenkilde and Bagger, 1948). Elisabeth Hartmann did an excellent job of discussing Scandinavian giants and their relationship to other supernatural beings in Scandinavia and throughout Northern Europe: see her Die Trollvorstellungen in den Sagen und Märchen der Skandinavischen Völker (Tübingen: Eberhard Karls Universität Tübingen, 1936). An excellent source dealing with the development of folklore theory together with extremely accessible introductory essays can be found in the late Alan Dundes's work, International Folkloristics: Classic Contributions by the Founders of Folklore (New York: Rowan and Littlefield, 1999).
I hope this helps.