Definition of "Rusian"

And finally, in keeping with the argument e silentio, one would be forced to conclude that the entire branch P of the Paterik Skitskij is of Rusian origin, i.e. that its chapters A–1 and B–G were added in Rusian translation to the body of chapters 2–22 and H–J transmitted in South Slavic manuscripts, so that the syntax, lexicon and morphology of the Story of the Merciful Nestor should be evaluated as Rusian.

1992, William Veder, The Merciful Nestor and Sozomen: Early Rusian Text Transmission in a Stratigraphic Perspective