2. What is the Hebrew for "Red Sea," then? I b'lieve the same expression can refer to either.
Dan
There is some confusion. The Reed Sea is mentioned, and the Red Sea.
I heard it years ago; I don't have a source. It may be completely false. Mea culpa.
Why, then, would the pre-Christian Septuagint have eruthra thalassa (Red Sea)?
No idea. You would agree, though, that suf in Hebrew means "reeds" (cf. Ex. 2:3, 5), and not "red"?
2. What is the Hebrew for "Red Sea," then? I b'lieve the same expression can refer to either.
Modern Israelis call the Red Sea yam suf, but that may be because generations of Bible translators have conflated the Sea of Reeds with the Red Sea. I know of no ancient sources which identified that body of water by name. (Just as there is no ancient Hebrew name for the Mediterranean; the modern Israeli name yam ha-tichon ("middle sea") is a literal translation of "Mediteranean."