Usage: 2 forms in 2 verses
Form Translated As     In Verse(s)
οίκτου of lament LXX.Jer.9.19
οίκτον a lamentation LXX.Jer.9.20

Liddell-Scott-Jones

οἶκτος (oiktos) a lament G:N-M

οἶκτος, ,

(οἴζω) pity, compassion, οἶ. δ᾽ ἕλε λαὸν ἅπαντα [Refs 8th c.BC+]; οἶ. τις ἴσχει ἀποκτεῖναι a feeling of pity prevents him from.., [Refs 5th c.BC+]: with genitive objecti, compassion for.., πόθος καὶ οἶ. τῆς πόλιος [οἶκτος εἰσιδών. ">Refs 5th c.BC+]

__2 lamentation, piteous wailing, [Refs 5th c.BC+] by the wailings of the sufferer, [Refs 5th c.BC+]