LTReikšminiai žodžiai: Baltiški rusų hidronimai; Baltų kalbos; Daryba; Hidronimai; Hidronimas; Hidronimų kilmė; Liaudies etimologija; Lietuvių hidronimai; Okos upės baseinas; Rusų hidronimai; Semantinės hidronimų grupės; Slavų kalbos; Baltic languages; Folk etymology; Hydronym; Hydronyms; Lithuanian hidronyms; Oka basin; Origin of hydronyms; Russian hydronyms; Russian hydronyms of Baltic origin; Semantic groups of hydronyms; Slavonic languages; Word formation.
ENA considerable number of the Russian hydronyms of the Oka basin are of Baltic origin. In terms of word formation they coincide exactly with the corresponding Lithuanian hydronyms or at least their bases. Three semantic groups of such hydronyms can be distinguished: (1) hydronyms, containing names of animals; (2) hydronyms, containing plant names; (3) hydronyms, derived from words in some way defining the hydronym or having to do with water.