Νεῖλος

Neilos: a city in Egypt. Hekataios in his Periegesis of it: ‘and a sanctuary of the river Neilos’. The ethnonym of the city is ‘Neilopolites’. But if the city alone is named Neilos, its ethnonym ought to follow the possessive derived from the river, ‘Neilaios’, as Apollonios says: ‘For all possessives in which what precedes the ι forms either the genitive or the nominative of the primitive noun are expressed with ι alone: “Poseidonios”, “Helikonios”, “Rhodios”, “Sakios”. But those whose penult naturally contains a diphthong never produce the form under discussion; for neither “kepaios” nor “Neilaios” is correspondingly accepted as an ethnonym.’