[Toybox] off-topic: /sbin --- "static" or "system"

[enh]

do you have a canonical reference to the first unix with an /sbin? the
question came up of what the "s" originally stood for. i'd always
believed "static" because that's what the old-timers told me when i
first came across unix in 1993. finding the first unix with /sbin
might lead to a proper answer.

since a post on the busybox list came up on my attempts to search for
the answer, i thought i'd ask...