Discusses accentuation rules for trisyllabic words and adjectives in -ιος/-ιo, especially ethnic and local names becoming proparoxytone when the i is short or due to certain consonant clusters, with many examples and citations.
ὀξύνεται. καὶ τὸ μονιός ὀξύνεται τρισύλλαβον, εἰ δὲ τὸ 'υ' πλεονάσῃ, προπαροξύνεται. μούνιος γάρ. Ὅσα ἀπὸ τῶν εἰς 'ξ' ἢ 'ψ' ἢ 'ρ' γίνεται διὰ τοῦ 'ι' βραχέος, προπαροξύνεται, εἰ μὴ ἐπὶ κυρίου διαστολή τις γένηται ἐν τρισυλλάβοις τριβράχεσιν ὥσπερ ἔχει τὸ Φρυγίος καὶ Φλογίος. καὶ προπαροξύνεται δὲ ταῦτα· Θρηΐκιος· λέγεται καὶ διὰ μακροῦ τοῦ 'ι' «ἀνέρα δὲ Τροίη Θρηΐκιον οὔτι φορήσει». Κιλίκιος, Φαιάκιος, Ναρύκιος, Νυράκιος, Νωράκιος, Κοράκιος, Φοινίκιος, Ζαρήκιος, Ἀτράκιος, Ῥάγιος, Μηνίγγιος, Ἀράβιος, Κινύφιος, Αἰγιλίπιος, Αἰθιόπιος. Εὐριπίδης Ἐρεχθεῖ «Αἰθιοπίαν νιν ἐξέσως´ ἐπὶ χθόνα». μακάριος, σωτήριος, ἀέριος, αἰθέριος. τὸ δὲ Ἰλλυριός οὐκ ἀντίκειται. οὐ γὰρ τὸ Ἰλλυριός παρὰ τὸ Ἴλλυρ. Τὰ διὰ τοῦ 'ιος' ἐθνικὰ ἢ τοπικὰ προπαροξύνονται, Ῥόδιος, Σάμιος, Κύπριος, Αἰγύπτιος, Δήλιος, Ἀψίνθιος, Πύλιος, οὐράνιος, θαλάσσιος, ἐντόπιος, ἐκτόπιος, ἐνδάπιος, ἐγχώριος καὶ ἐπιχώριος, τὸ χώριος μὲν οὐ λέγεται, ἀλλὰ τὰ σύνθετα. τὸ ἐγχώριος καὶ παρὰ Σοφοκλεῖ κεῖται (Oed. Col. 875). τὸ δὲ ἐπιχώριος καὶ ἐπιχωριάζειν ἐν τῷ περὶ ψυχῆς φησι Πλάτων (c. 1). ἐγκώμιος. Ἡσίοδος «εἰ γάρ τοι καὶ χρῆμ´ ἐγκώμιον ἄλλο γένοιτο». Ἄβιος ἔθνος Σκυθικόν. Ὅμηρος (Il. Ν 6) «Γλακτοφάγων Ἀβίων τε, δικαιοτάτων ἀνθρώπων». Ἀλέξανδρος δὲ ἐν τῷ περὶ Εὐξείνου πόντου φησίν, ὡς Διόφαντος εἶπεν, οὕτω λέγεσθαι αὐτοὺς διὰ τὸ τὸν Ἀβιανὸν ποταμὸν κατοικεῖν. ἢ ὅτι βίῳ ἑδραίῳ οὐ χρῶνται οὕτω λέγονται, διὰ τὸ ἐφ´ ἁμαξῶν φέρεσθαι. Δίδυμος δὲ Θρᾴκιον ἔθνος φησίν. Αἰσχύλος δὲ Γαβίους διὰ τοῦ 'γ' ἐν λυομένῳ Προμηθεῖ ἔπειτα δ´ ἥξεις δῆμον ἐνδικώτατον βροτῶν ἁπάντων καὶ φιλοξενώτατον, Γαβίους, ἵν´ οὔτ´ ἄροτρον οὔτε γατόμος τέμνει δίκελλ´ ἄρουραν, ἀλλ´ αὐτοσπόροι γύαι φέρουσι βίοτον ἄφθονον βροτοῖς.
It is accented with an acute. And μονιός too is accented with an acute when it is trisyllabic; but if the ‘υ’ is added, it is accented with a proparoxytone: for μούνιος.
Whatever is formed from words ending in ‘ξ’ or ‘ψ’ or ‘ρ’ by means of a short ‘ι’ is accented with a proparoxytone, unless in proper names some distinction arises in trisyllables with three short syllables, as is the case with Φρυγίος and Φλογίος. And these too are accented with a proparoxytone: Θρηΐκιος; it is also said with long ‘ι’: «ἀνέρα δὲ Τροίη Θρηΐκιον οὔτι φορήσει». Κιλίκιος, Φαιάκιος, Ναρύκιος, Νυράκιος, Νωράκιος, Κοράκιος, Φοινίκιος, Ζαρήκιος, Ἀτράκιος, Ῥάγιος, Μηνίγγιος, Ἀράβιος, Κινύφιος, Αἰγιλίπιος, Αἰθιόπιος. Euripides in the Ἐρεχθεύς: «Αἰθιοπίαν νιν ἐξέσως´ ἐπὶ χθόνα».
μακάριος, σωτήριος, ἀέριος, αἰθέριος. But Ἰλλυριός is not an exception; for Ἰλλυριός is not derived from Ἴλλυρ.
Ethnics or toponyms in -ιος are accented with a proparoxytone: Ῥόδιος, Σάμιος, Κύπριος, Αἰγύπτιος, Δήλιος, Ἀψίνθιος, Πύλιος, οὐράνιος, θαλάσσιος, ἐντόπιος, ἐκτόπιος, ἐνδάπιος, ἐγχώριος and ἐπιχώριος; χώριος itself is not used, but only the compounds. ἐγχώριος is found also in Sophocles (Oed. Col. 875). And ἐπιχώριος and ἐπιχωριάζειν Plato mentions in the treatise On the Soul (c. 1).
ἐγκώμιος. Hesiod: «εἰ γάρ τοι καὶ χρῆμ´ ἐγκώμιον ἄλλο γένοιτο».
Ἄβιος, a Scythian people. Homer (Il. Ν 6): «Γλακτοφάγων Ἀβίων τε, δικαιοτάτων ἀνθρώπων». But Alexander in his work On the Euxine Sea says, as Diophantus stated, that they are so called because they dwell by the river Ἀβιανός; or else they are so called because they do not live a settled life, since they are carried about on wagons. Didymus, however, says they are a Thracian people.
Aeschylus, however, has Γαβίους with gamma in the Prometheus Unbound: “and then you will come to a people most just of all mortals and most hospitable, the Γαβίοι, where neither plough nor mattock cuts the clod of the field, but self-sown earth bears abundant livelihood for mortals.”