Rules for accentuation of neuter nouns ending in -ον; treatment with surrounding vowels/diphthongs (α, αυ, υ, οι, ωι), proparoxytone/oxytone tendencies, examples including place-names and common nouns.
συνήθεια, τὸ γὰρ ἐπιθετικὸν κηρύκειον τὸν τοῦ κηρύκειος τόνον ἐφύλαξε καὶ τὸ κύριον προπαροξύνεται. τὸ δὲ ὠκυτόκειον καὶ ἄλλα σύνθετα προπαροξύνεται. * Τὰ εἰς 'ον' καθαρὸν παραληγόμενα τῷ 'α' σπάνια ὄντα βαρύνεται, Μέταον πόλις Λέσβου, ἣν Μέτας Τυρρηνὸς ᾤκισεν, ὡς Ἑλλάνικος. * Τὰ εἰς 'ον' παραληγόμενα τῇ 'αυ' διφθόγγῳ σπάνια ὄντα βαρύνεται, Σαῦα κώμη τῆς εὐδαίμονος Ἀραβίας, Ἄναυα πόλις Φρυγίας, ὡς Ἡρόδοτος ( 7, 30). Τὰ εἰς 'ον' καθαρὸν παραληγόμενα τῷ 'υ' βαρύνεται, πτύον, βρύον, πύον τὸ ἔμπυον τὸ καὶ πυός. θρύον· ἔστι καὶ πόλις τῆς Μεσσηνίας ἐκ τῶν ἐν αὐτῇ φυομένων θρύων ὁμωνύμως τῷ φυτῷ λεγομένη. λέγεται δὲ ἀπὸ φυτοῦ Θρυόεις καὶ Θρυόεσσα. θύον ὃ καὶ θύος λέγεται. Κύον πόλις Καρίας. Ἀπολλώνιος τετάρτῃ Καρικῶν, μεθ´ ὧν καὶ γυῖον τῇ 'υι' διφθόγγῳ παραληγόμενον καὶ οὐκ ἔχον ὁμοίου παράθεσιν. κάρυον, κρόμμυον, δίκτυον, ἔμβρυον, δάκρυον, κρήγυον, ἄρκυον, μήνυον εἶδος ἄνθους, γεράνδρυον, μεσόφρυον, ἔνδρυον, γήθυον τὸ ἀμπελόπρασον. Ἔγγυον πόλις Σικελίας. Τὰ εἰς 'ον' δισύλλαβα παραληγόμενα τῇ 'οι' διφθόγγῳ ὀξύνεται, γλοιόν, τὸ τοῖς πώγωσι τῶν τράγων ἐπισυναγόμενον ἀπὸ τῆς ὕλης, Κροιόν ὄνομα ὄρους. βοιόν τῶν πεντήκοντα ἐτῶν ἀριθμός. ἔστι καὶ Βοιόν Δωρικὴ πόλις, ἣ καὶ θηλυκῶς λέγεται, μοιόν τὸ αἰδοῖον. τὸ δὲ πλοῖον προπερισπᾶται ὡς πάσχον διαίρεσιν αἰολικῶς. πλόϊον γὰρ λέγεται. Τὰ εἰς 'ον' δισύλλαβα μονογενῆ παραληγόμενα τῷ 'ω' μετὰ τοῦ 'ι'
Usage: for the adjectival κηρύκειον has preserved the accent of κηρύκειος, and the proper noun is accented on the antepenult. But ὠκυτόκειον and other compounds are accented on the antepenult.
Those ending in -ον with a pure α in the penult, being rare, are barytone: Μέταον, a city of Lesbos, which Metas the Tyrrhenian founded, as Hellanicus says.
Those ending in -ον with the diphthong αυ in the penult, being rare, are barytone: Σαῦα, a village of Happy Arabia; Ἄναυα, a city of Phrygia, as Herodotus (7, 30).
Those ending in -ον with a pure υ in the penult are barytone: πτύον, βρύον, πύον, “pus,” also πυός. θρύον: there is also a city of Messenia, named, from the θρύα that grow in it, homonymously with the plant. From the plant are also formed Θρυόεις and Θρυόεσσα. θύον, which is also called θύος. Κύον, a city of Caria. Apollonius in the fourth book of his Carica; among these also γυῖον, with the diphthong υι in the penult and having no parallel citation. κάρυον, κρόμμυον, δίκτυον, ἔμβρυον, δάκρυον, κρήγυον, ἄρκυον, μήνυον, a kind of flower; γεράνδρυον, μεσόφρυον, ἔνδρυον, γήθυον, “vine-leek.” Ἔγγυον, a city of Sicily.
Disyllables ending in -ον with the diphthong οι in the penult are oxytone: γλοιόν, the matter that collects on the beards of goats from the wood; Κροιόν, the name of a mountain; βοιόν, the number of fifty years. There is also Βοιόν, a Doric city, which is also said in the feminine; μοιόν, the pudendum. But πλοῖον has the circumflex on the penult, as undergoing division in Aeolic fashion; for πλόϊον is said.
Disyllabic, single-gender words ending in -ον with ω in the penult together with ι…