[citation needed] The endonym Vâsi [waˈsi] is ultimately cognate with Kamviri Přâsü̃ [pɽaˈsỹ] (whence the name Prasun) and Katë Přâsiu [pɽaˈsju].

[5] Prasun is a language spoken by the Vâsi (Prasuni) people who are located in the Pârun Valley, known as Vâsi-gul, at the beginning of the Pech River basin in Nuristan Province of northeastern Afghanistan.

The central dialect, üšüt-üćü-zumu-vari, is spoken in the middle four villages, Seć (Pronz), Üćü (Dewa), Üšüt (Kshtoki), and Zumu.

[6] One characteristic feature defining all Prasun dialects is the shift of ancient *d to l, which was lost in intervocalic position in other Nuristani languages, such as vazala [wɘˈzɘlɘ] "shoe", compared to Ashkun vâćâ [vaˈt͡sa], Kamviri vâćo [vaˈt͡so], and Nuristani Kalasha oćä [oˈt͡sæ], and the pervasive lenition of initial stops, such as viṭa [wiʈɘ] "wing", compared to Ashkun pâṭu [paˈʈu] "feather", Kamviri pâṭü [paˈʈy] "feather", and Nuristani Kalasha paṭä [paˈʈæ] "feather, wing".

Prasun is part of the Nuristani branch of the Indo-Iranian languages, which show both Iranian and Indo-Aryan influences, but are otherwise not closely related.