Usage: 2 forms in 3 verses
Form Translated As     In Verse(s)
μαντείον An oracle LXX.Prov.16.10
oracle LXX.Ezek.21.22
μαντεία oracles LXX.Num.22.7

Liddell-Scott-Jones

μαντεῖον (manteion) an oracle G:N-N

μαντεῖον-εῖον,

Ionic dialect and Epic dialect μαντεῖον-ϊον, τό, oracle, i.e.,

__I oracular response, mostly in plural, μαντεῖονϊα Τειρεσίαο [Refs 8th c.BC+]
__II seat of an oracle, [Refs 5th c.BC+]: in plural of a single shrine, [Refs 5th c.BC+]
__III method, process of divination, [Refs]
__IV in plural, rewards of divination, [LXX]

LSJ Scripture Refs: LXX.Num.22.7