There are a number of ancient Greek proper nouns suffixed with -οῦς(α/αι), of which the etyma are often clear
e.g.
Τραπεζοῦς (Trapezus) etym. τράπεζα
Ὑδροῦς (Hydrus) etym. ὕδωρ
Ἰχνοῦσα (Ichnusa) etym. ἴχνος
Ὀφιοῦσα (Ophiusa) etym. ὄφις
Πιθηκοῦσαι (Pithecusae) etym. πίθηκος
Πελαγοῦσαι (Pelagusae) etym. πέλαγος
What kind of inflection/nomenclature is this?
e.g.
Τραπεζοῦς (Trapezus) etym. τράπεζα
Ὑδροῦς (Hydrus) etym. ὕδωρ
Ἰχνοῦσα (Ichnusa) etym. ἴχνος
Ὀφιοῦσα (Ophiusa) etym. ὄφις
Πιθηκοῦσαι (Pithecusae) etym. πίθηκος
Πελαγοῦσαι (Pelagusae) etym. πέλαγος
What kind of inflection/nomenclature is this?