Meta originally meant Alt, not Win/Super/GUI.
Are you sure? I'm no keyboard historian, but I was under the impression that the ◇/meta key was analogous to the Windows key.
I think Emacs maps M-key to Alt (not an Emacs user myself). However, on HHKB meta is mapped to win/command, no?
On the Space-cadet keyboard, the order "of apparition" seems to be Ctrl, Meta, Super and Hyper.
Anyway... I think Meta (written out) would probably look better combined with Fn/Menu, which won't be used here. So, either way.
I mean, it's debatable because there is no 1–1 mapping between the old Ctrl, Meta, Super, Hyper and the modern Ctrl, Alt, GUI. Technically all of them can co-exist on a single keyboard (and, indeed, X on Linux supports all six). I mainly refer to the Emacs usage because it's pretty much the only consistent, direct link that's been around for as long as all of those keys have.
“Originally” is the wrong way of putting it, though, you're right about that; my bad. “Most closely matching” is a more accurate description.
Edit: re HHKB: That uses an empty diamond (♢), which is sometimes used to mean Super, whereas Meta is usually represented with a filled diamond (
♦).