Quoting Daniel Taylor (random@???):

> I thought it was "system"....

Could be -- but as, in effect, a synonym for superuser.

, but I don't even know who originated the
> separation.

Thompson and Ritchie, as a kludge to deal with the need to span two disk
packs on their PDP-11, back in 1971. (Subsequent functional use for
the split of course differs.)

Upthread, I provided the link to my friend Rob Landley telling the
anecdote about that '71 kludge.

> As for the "statically linked binaries in /sbin", that may come from
> the (formerly?) common practice of having all the binaries needed
> for system startup statically linked in case something happened to
> /lib.

Seems farfetched. Also, I've been in *ix for a long time, and haven't
heard that particular concern.