EN
In Indo-European there were at least two feminine gender forms of the *-u-stem adjectives: a stem in *-i//ya- as well as a stem in *-u(//wa?)-. It appears probable that both continue forms with a single feminine gender marker *-(y)a//a- added to the root extended or not with *-u-. Since the Common Slavic adjectives *plyt(7)v7 and *plyt7k7, where 7 stands for a high reduced back vowel called 'jer', surviving in the historical Slavic languages, seem to go back to an ancient *-u-stem adjective *plutu-, it is reasonable to look for some traces of *-u-stem inflection (in particular, of its feminine gender forms) in older layers of the Slavic hydronymy in Poland. It is argued in the present paper that the simplest and most elegant way of explaining etymologically the river names Plycwia (Central Poland) and Plytwica (name of two rivers in Northern Poland) is to trace them back to the preforms, respectively, *plytv(j)i (gen. sg. *plytvje), a feminine form of *plyt7 (gen. sg. *plytvu) and *Plyt7vica, the latter derived from another feminine form *plyty (gen. sg. *plyt7ve).