Usage: 2 forms in 3 verses
Form Translated As     In Verse(s)
μήνισ his vehement anger LXX.Isa.16.6
their vehement anger LXX.Gen.49.7
μήνιν vehement anger LXX.Num.35.21

Liddell-Scott-Jones

μῆνις (mēnis) vehement anger G:N-F

μῆνις,

Doric dialect and Aeolic dialect μᾶν-, , genitive μήνιος [Refs 5th c.BC+]:—wrath; from [Refs 8th c.BC+] downwards frequently of the wrath of the gods, [Refs 8th c.BC+]; μῆνιν ἔχειν ἀπὸ θεοῦ Vett.[Refs 5th c.BC+]; also of the dead worshipped as heroes, τοῖσι μ. κατέσκηψε Ταλθυβίου [Refs 5th c.BC+]; of injured parents, [Refs 4th c.BC+]; of suppliants, [Refs 5th c.BC+]: but also, generally, of the wrath of Achilles, [Refs 8th c.BC+]; of the revengeful temper of a people, [Refs 8th c.BC+]