Historical Explanation for *pi as Plural and Proximate and Nominalizer

[R. Rankin]

> It would be interesting to check on the etymology of
> opha 'to join' as well. Maybe all three forms, i.e.
> -pi, ob, and opha, are, ultimately, related. The
> semantic fit of ob 'with' and opha 'to join' is just
> to close to be neglected, at least to me.

I wonder if there are other instances of aspirates reducing to voiced stops (or
nasals) word- or syllable-finally?  I know this happens to /p, t, k/ --> /b,
l/d, g/, but I'm a little surprised to see it with /ph/.  I'm no Dakotanist
though, so I defer to you guys on these sound changes.

The only /ophE/ I know of in Dhegiha is the verb 'step, tread, follow a path'.
I'll look for 'join'.

Bob