Difference between Hermetism and Hermeticism

from a Facebook discussion in a Golden Dawn, in answer to a question about how contemporary occultists define Hermeticism:

There's a useful distinction between Hermetism (the late antique religion of Hermes Trismegistus) and Hermeticism (post-renaissance revivals of the Hermetic texts) ... interestingly "Hermetic" ends up applied to both. One rarely encounters a definition of "Hermeticism" in contemporary practice that has much to do with the texts or world-view of ancient "Hermetism." Check out the studies of Garth Fowden (The Egyptian Hermes), Florian Eberling (The Secret History of Hermes Trismegistus), Antoine Faivre (The Eternal Hermes), and Brian Copenhaver's introduction to his Hermetica translation, for more information about how current scholars define Hermetism/Hermeticism. In my view occult definitions of Hermeticism should be built on the best research--otherwise it's hard to rely on any sense that there's any continuity to the "Hermetic" tradition--but I don't often see that happening to the degree that I would like. I'm still waiting for a satisfactory explanation of exactly what, for example, the Golden Dawn authors meant by "Hermetic."