115. Stems in -τ, -δ, -θ after unaccented -ῐ̄- or -υ- lose the mute and take -ν in the accusative singular, as if they were stems in -ι or -υ (130).
ἡ κόρυς, κόρυθ-ος, acc. κόρυν (helmet)
116. The vocative of παῖς, παιδ-ός (child) is παῖ. The stem was originally παϊδ-; hence the irregular accent (101 and 101.a).
παῖς, παίδων, παίδοιν