Where did Ruym come from?

I have to say that this one always baffled me. Thanks to the wonder of Google I have discoved that "Ruym" was in fact an ancient name of Thanet - It was Anthony John that put me on to Ruym as a place name. And of course gate comes from the ancient Egyptian "khet" meaning gate, in particular gate to the sea (as in Margate), or in fact gate to Thanet as in Ramsgate.
"Our word gate is the Egyptian khet, which, in relation to the water, is a ford, port, or harbour; khet, a port, to navigate, go, stop, be enclosed. This supplies the water-gate as in Margate and Ramsgate. Mer (Eg.) is the sea and also a land-limit, the boundary of a region on the water. Mer-gate (Margate) is the gate at the limit of Thanet at the north-east extremity of the isle. Ruim or Ruym[5] is an ancient British name of Thanet. Ramsgate is the gate of Ruim. Ru (Eg.) is an outlet, waterway. Ima or im is the sea. Ruim is the mouth or outlet to the sea. The gate in Ramsgate is a repetition of the ru in Ruim; according to the reduplicative mode of compounding the later names, Ramsgate, the sea-gate of Thanet, is already expressed by the ancient name of Ruim or Ruima." This quotation was taken from "A Book of the Beginnings".