Is declension too speculative.
Fragment of a discussion from User talk:Rua
So, you'd add a Narten grade and what else? I'm not sure I see any options for the long oblique stems besides leveling, substratum borrowing, or a sneaky *h₁ in the stem. The oblique oxytones from monosyllabic nouns in AG are somewhat uncommon, as evinced by Newt having to add a parameter obloxy=
to an early version of {{grc-decl}}
to deal with πούς and θήρ. Speaking of *ǵʰwer- and θήρ, which would act as a fair comparison for this situation, what do we think there? I will need to look at my reference material later to see what Beekes and De Vaan say about them.