-o

The neuter NAsg of consonant stems, i-stems and u-stems are
endingless, but that of o-stems (thematic stems) is -m. That -m might
be from a 'lost case'(?), originally with partitive meaning, surviving
in Gpl. If the neuter NAsg of o-stems was originally endingless, the
3sg perf middle (impersonal) ending -to is actually an old endingless
ppp in *´-to, and that pesky Slav neuter NAsg -o might descend from it
too.


Torsten