Comments: Ub. 3d p. a-pstá-n. Dumézil 1975 considers the Ub. word as a loan from Adygh., deriving the Adygh. verb from psǝ 'water'; Shagirov 2,36 also supports this etymology. It is possible, but seems to us less likely in view of the external evidence.
Since there are no AA parallels, it is impossible to distinguish between reconstructing *-š- or *-s- in the root.
