8 again.

[R. Rankin]

Makes sense.  Whereas in Greek it was an alternative to the digraph, <ou>, in
Cyrillic the early /u/ used 8 as the norm.  The oldest Cyrillic "u"s used
something very like <8>, but with the circle in the lower half smaller than the
"cup" on top.  Ultimately it evolved into the current "y".

> Someone has published on the origin of 8. I can't recall who it was,
> unfortunately. It is even known what year it arrived in French
> orthography. I believe it came from Russia, but that part's fuzzy.