Accentuation rules for Ancient Greek genitives and adjectives: pleonasm of ε affecting oxytone/paroxytone positions; examples of forms in -τεος, -ετός, -ος, and -αλεος; possessive genitives causing proparoxytone accents.
δὲ ὁ λοχεός ἔσται κατ´ ὀξεῖαν τάσιν «ὁ δ´ ἐκ λοχεοῖο πάϊς» (Hesiod. theog. 178). ἀλλ´ οὖν γε βαρυτόνως οἱ πλείους ἀνέγνωσαν πλεονασμὸν ἐκδεξάμενοι τοῦ 'ε', ὥστε παρὰ τὴν λόχου γενικὴν «ἐκ λόχου ἀμπήδησε» (Il. Λ 379) λόχοιο γενέσθαι καὶ λοχέοιο. παρὰ κηδεύω δὲ κηδεός, κελεύω Κελεός ὄνομα κύριον. ὠρεύω Ὠρεός πόλις Εὐβοίας. τούτοις ἀκόλουθον καὶ τὸ θυρεός μὴ παρὰ ῥῆμα γενόμενον. Τὰ εἰς 'τεος' παροξύνεται, εἰ μὴ ἐκ πλεονασμοῦ ἔχοι τὸ 'ε' ἢ κτητικὰ εἴη, ῥητέος, πρακτέος, ἀθροιστέος, μεμπτέος, γραπτέος, λαλητέος, νοητέος, ποιητέος, γνωστέος. τὸ δὲ ἐτεός ὀξύνεται. ἀπὸ γὰρ τοῦ ἐτός ὀξυτόνου, ὃ σημαίνει τὴν ὕπαρξιν, ἐξ οὗ τὸ ἀληθές, ἐν πλεονασμῷ τοῦ 'ι' γέγονεν ἐτεός ὀξείᾳ τάσει. ἐπὶ γὰρ τῶν εἰς 'ος' ὀνομάτων ὁ πλεονασμὸς τοῦ 'ε' φυλάσσει τὴν ἐπὶ τέλους ὀξεῖαν, κενός κενεός, ἀδελφός ἀδελφεός, δαφοινός δαφοινεός. τὸ δὲ δρακόντεος, γερόντεος κτητικά ἐστι. Τὰ διὰ τοῦ 'αλεος' παραγωγὰ ὑπὲρ τρεῖς συλλαβάς ἐστι καὶ παροξύνεται, χωρὶς εἰ μὴ ἔνδειαν ἔχῃ τοῦ 'ι' ἀπὸ κτητικοῦ ὀνόματος οἷον νηφαλέος, αὐαλέος, σμερδαλέος, θαρσαλέος, σκωπαλέος, δειμαλέος, κερδαλέος, φρικαλέος, ἀργαλέος, φοιταλέος, γηραλέος, λευγαλέος, ὀπταλέος, ἰκμαλέος, ῥωμαλέος, ῥωγαλέος, καρφαλέος, ἁρπαλέος. πρόσκειται «εἰ μὴ ἔχῃ ἔνδειαν τοῦ 'ι' ἀπὸ κτητικοῦ ὀνόματος» διὰ τὸ δαιδάλειος δαιδάλεος, ἔνθεν αἰτιατικὴ «δαιδάλεον θώρηκα» παρὰ τῷ ποιητῇ (Θ 195), κονισάλειος κονισάλεος παρὰ Ἀντιμάχῳ «τὼ δ´ αὖτ´ ἀμφὶ κονισάλεον πεπονήατο δίφρον». ὅσα δὲ ἀπὸ τῶν κτητικῶν ἐγένετο κατ´ ἔνδειαν τοῦ 'ι', καὶ προπαροξύνονται, Ἀγαμεμνόνεος, Ἑκτόρεος, Νεστόρεος, τέλεος, χάλκεος, χρύσεος, τέγεος, κήλεος. Ὑπερβόρεοι, ἔθνος, ὃ
But λοχεός will have an acute accent: «ὁ δ´ ἐκ λοχεοῖο πάϊς» (Hesiod. theog. 178). However, most people read it with a grave accent, accepting an addition of the 'ε', so that alongside the genitive of λόχος, «ἐκ λόχου ἀμπήδησε» (Il. Λ 379), there came to be λόχοιο and λοχέοιο. From κηδεύω comes κηδεός; from κελεύω, Κελεός, a proper name. From ὠρεύω, Ὠρεός, a city of Euboea. In accordance with these is also θυρεός, not formed from a verb.
Words in -τεος are accented on the penult, unless they have the 'ε' by addition or are possessive: ῥητέος, πρακτέος, ἀθροιστέος, μεμπτέος, γραπτέος, λαλητέος, νοητέος, ποιητέος, γνωστέος. But ἐτεός is accented with an acute. For from ἐτός, accented with an acute, which signifies existence (whence ἀληθές), by addition of the 'ι' there has arisen ἐτεός with an acute accent.
For in nouns in -ος the addition of the 'ε' preserves the final acute: κενός, κενεός; ἀδελφός, ἀδελφεός; δαφοινός, δαφοινεός. But δρακόντεος and γερόντεος are possessives.
Derivatives formed with -αλεος are more than three syllables and are accented on the penult, except when they have loss of the 'ι' from a possessive noun, as: νηφαλέος, αὐαλέος, σμερδαλέος, θαρσαλέος, σκωπαλέος, δειμαλέος, κερδαλέος, φρικαλέος, ἀργαλέος, φοιταλέος, γηραλέος, λευγαλέος, ὀπταλέος, ἰκμαλέος, ῥωμαλέος, ῥωγαλέος, καρφαλέος, ἁρπαλέος.
The clause “except when it has loss of the 'ι' from a possessive noun” is added because of δαιδάλειος, δαιδάλεος, whence the accusative «δαιδάλεον θώρηκα» in the poet (Θ 195), and κονισάλειος, κονισάλεος in Antimachus: «τὼ δ´ αὖτ´ ἀμφὶ κονισάλεον πεπονήατο δίφρον». But those that have arisen from possessives by loss of the 'ι' are also accented on the antepenult: Ἀγαμεμνόνεος, Ἑκτόρεος, Νεστόρεος, τέλεος, χάλκεος, χρύσεος, τέγεος, κήλεος. Ὑπερβόρεοι, a people, who…