Variation of -ρος endings: alternation between ει diphthong and long ι in names and nouns (place-names, ethnics), with examples and Homeric citations.
Τὰ εἰς 'ρος' ὑπὲρ δύο συλλαβὰς παραληγόμενα τῇ 'ει' διφθόγγῳ ἢ μόνῳ τῷ 'ι' ἐκτεταμένῳ βαρύνεται, Κάμειρος τὸ κύριον—ἔστι δὲ παῖς Κερκάφου τοῦ Ἡλιάδου καὶ Κυδίππης—διὰ διφθόγγου, Κάμιρος δὲ πόλις ἐν Ῥόδῳ διὰ τοῦ 'ι' «Λίνδον Ἰήλυσόν τε καὶ ἠνεμόεντα Κάμιρον» (Il. Β 656). ἤπειρος, Κάβειρος πόλις τῆς κάτω Ἀσίας. τοὺς δὲ δαίμονας Καβείρους ὁ Ἀλεξίων διὰ τοῦ 'ι', ὡσαύτως δὲ Φιλόξενος. ἡ δὲ παράδοσις δίφθογγον ἔχει καὶ ἴσως συνέδραμε τῷ μάγειρος, αἴγειρος, πέπειρος, ὄνειρος. Ἄνδειρος ὄνομα ποταμοῦ, Κόνειρος ὄνομα ἔθνους, ὄνειρος, πέπειρος, μάγειρος παρὰ τὸ μάσσω ὁ τὰς μάζας φυρῶν. Αἰολεῖς δὲ διὰ τοῦ 'ι'. αἴγειρος διὰ διφθόγγου τὰ δύο. εὕρηται γὰρ καὶ χωρὶς τοῦ 'ι' οἷον «καὶ αἰγέρων ἔφυσαν εὐγενέστεραι» καὶ κατὰ πλεονασμὸν τοῦ 'ι' αἴγειρος Ὅμηρος (Od. η 106) «μακεδνῆς αἰγείροιο». τὰ γὰρ εἰς 'ρος' ῥηματικὰ τῇ 'ει' διφθόγγῳ θέλουσι παραλήγεσθαι οἷον ἀΐσσω αἴγειρος, μάσσω μάγειρος, ὀνῶ ὄνειρος, πέπτω πέπειρος. τὸ δὲ 'αι' τῆς πρώτης συλλαβῆς γέγονεν ἀπὸ τοῦ ἀΐσσω κατὰ κρᾶσιν. ἔστι δὲ καὶ Αἴγειρος πόλις Μεγαρίδος, ὡς Θεόπομπος πεντηκοστῇ ἕκτῃ, ἣν Στράβων Αἰγείρουσαν λέγει. σάπφειρος λίθος, Στάγειρος. Κάσπειρος πόλις Πάρθων προσεχὴς τῇ Ἰνδικῇ καὶ τὸ ἐθνικὸν ὁμοφώνως. Στάλιρος, Σίτιρος, Βίστιρος πόλις Θρᾴκης καὶ Πίστιρος τὸ ἐμπόριον. Κύστιρος, Δύσιρος, Βεδύσιρος, ἄϊρος σύνθετον ἀπὸ δισυλλάβου Ἶρος «ἦ τάχα Ἶρος ἄϊρος
Nouns in -ρος, when their penult is more than two syllables from the end and is lengthened with the diphthong ει or with ι alone lengthened, are accented with a grave: Κάμειρος, the proper name—he is the son of Cercaphus the son of Helius and of Cydippe—with a diphthong; but Κάμιρος, a city in Rhodes, with ι: “Λίνδον Ἰήλυσόν τε καὶ ἠνεμόεντα Κάμιρον” (Il. Β 656). ἤπειρος; Κάβειρος, a city of Lower Asia. But Alexion writes the daimones Καβείρους with ι, and likewise Philoxenus. Tradition, however, has the diphthong, and perhaps it ran together with μάγειρος, αἴγειρος, πέπειρος, ὄνειρος. Ἄνδειρος is the name of a river; Κόνειρος, the name of a people; ὄνειρος, πέπειρος, μάγειρος from μάσσω, “the one who kneads the barley-cakes.” The Aeolians, however, write with ι. αἴγειρος is written with the diphthong in both syllables; for it is found also without ι, as in “καὶ αἰγέρων ἔφυσαν εὐγενέστεραι,” and with pleonasm of ι, αἴγειρος in Homer (Od. η 106): “μακεδνῆς αἰγείροιο.” For verbal nouns in -ρος want their penult to be with the diphthong ει, e.g. ἀΐσσω → αἴγειρος, μάσσω → μάγειρος, ὀνῶ → ὄνειρος, πέπτω → πέπειρος. But the αι of the first syllable has come from ἀΐσσω by crasis. There is also Αἴγειρος, a city of the Megarid, as Theopompus says in the fifty-sixth book, which Strabo calls Αἰγείρουσα. σάπφειρος, a stone; Στάγειρος. Κάσπειρος, a city of the Parthians near India, and the ethnic name likewise. Στάλιρος, Σίτιρος, Βίστιρος, a city of Thrace, and Πίστιρος, the trading-post. Κύστιρος, Δύσιρος, Βεδύσιρος; ἄϊρος, a compound from the disyllable Ἶρος: “ἦ τάχα Ἶρος ἄϊρος”