Usage: 3 forms in 4 verses
Form Translated As     In Verse(s)
ακούσιόν it is unintentional LXX.Num.15.25
ακούσιον an unintentional LXX.Eccl.10.5
unintentional LXX.Num.15.26
ακουσίων their unintentional LXX.Num.15.25

Liddell-Scott-Jones

ἀκούσιος (akousios) unintentional G:A

ἀκούσιος, ον

(also α, ον [Refs 2nd c.AD+], Ionic dialect and Epic dialect (also in anapaest meter, [Refs 5th c.BC+]; Attic dialect contraction ἀκούσιος [], ον, also in [Refs 3rd c.AD+]:— against the will, constrained, of acts or their consequences, καὶ τῷ οὔ κως ἀεκ. ἐγίνετο τὸ ποιεύμενον[Refs 6th c.BC+]; often in Attic dialect of involuntary offences, . φόνος[Refs 5th c.BC+]; πράκτορες τῶν ἀκουσίων [Refs 5th c.BC+]. adverb -ίως[Refs 4th c.BC+]

__II of persons, only in adverb ἀκουσίως involuntarily, [Refs 5th c.BC+]; . ἀποθανεῖν, opposed to ἑκουσίως ἀποκτείνειν, [Refs 5th c.BC+]; . τινὶ ἀφῖχθαι to have come as an unwelcome guest, [Refs 5th c.BC+]