Devi and Vrkis feminines

In Vedic Sanskrit, the  and inflections are two types of inflection of feminine ī-stems.

Vrkis
The inflection exhibits an ablaut pattern different from its counterpart, the Devī inflection. The distinguishing feature of this inflection is that the ī is always accented (excepting the Vocative), and that the Nominative singular has the desinence -s, like non-feminine words. Indeed, while -words are overwhelmingly of the feminine gender, there are a few members of the class that belong to the masculine gender, or are gender indeterminate, e.g.  "wain-driver, charioteer" (often applied to Agni, who trafficks sacrificial offerings and divine boons between mortals and immortals).

The inflectional type is usually accepted to reach back into Proto-Indo-European times, with an exact correspondence of Sanskrit  and Old Norse ylgr, both meaning "she-wolf", first described by Karl Verner in 1877 (see Verner's law). The distinction between Devi and Vrkis dies out in during the Vedic period, and Pāṇini is not aware of it, classifying the ī-stems by their accentuation (Vrkis words are a subset of NīS).

One formation that has been diachronically connected with the Vrkis inflection is Cvi, which in Pāṇini's grammar of Classical Sanskrit refers to a formation where an ī is added to a nominal stem and compounded with a verbal root kr "to make", as "to be" or bhū "to become", resulting in a factitive verb where the ī-stem is indeclinable and used like a preverb. For example, grāmī-bhū "to get possession of a village" (from grāma "village").

Devi
The Devi inflection exhibits an ablaut pattern different from its counterpart, the Vrkis inflection. Pāṇini does not make the distinction, classifying the ī-stems by their accentuation (Devi words may be NiiN, NiiP or NiiS).