Lexical Definition

‎ἑκούσιον‎ hekoúsion (hek-oo'-see-on) voluntary G:A
neuter of a derivative from ‎ἑκών‎

willingly.

Usage: 7 forms in 15 verses
Form Translated As     In Verse(s)
ἑκούσιον willingness Phlm.1.14
εκούσιον a voluntary LXX.Num.15.3
as a voluntary LXX.Ps.68.9
voluntary LXX.Lev.7.16LXX.Ezra.3.5
εκούσια a voluntary LXX.Ezra.8.28
voluntary LXX.Ps.119.108LXX.Prov.27.6
your voluntary LXX.Num.29.39LXX.Deut.12.6
εκουσίων your voluntary LXX.Lev.23.38
εκουσίω our voluntary LXX.Neh.5.8
voluntary LXX.1Chr.28.21
εκουσίου voluntary LXX.Ezra.1.4
εκουσίοισ voluntary offerings LXX.Ezra.1.6

Abbott-Smith

ἐκούσιος, -ον (< έκών), [in LXX chiefly for נְדָבָה, as Nu 15:3 (κατ’ ἑ.);]
usually of actions, voluntary: κατὰ ἑ., of free will (Lft., in l), Phm 14.†

Abbott-Smith References

Book Refs
Numbers 15:3
Philemon 1:14

Liddell-Scott-Jones

ἑκούσιος-ος, α, ον

[Refs 5th c.BC+]; also ος, ον [Refs 5th c.BC+]: (ἑκών):—of actions, voluntary, πόνοι [Refs 5th c.BC+][same place]; φυγή E.[same place]; ἁμάρτημα [Refs 5th c.BC+]; ἀδικήματα [Refs]undertaken voluntarily, [Refs 2nd c.AD+]; τὰ . voluntary acts, opposed to τὰ ἀκούσια, [Refs 5th c.BC+]

__2 rarely of persons, willing, acting of free will, ἥμαρτεν οὐχ ἑκουσία [Refs 5th c.BC+]
__II adverb -ίως[Refs 5th c.BC+]; ἐξ ἑκουσίας (i.e. γνώμης) [Refs 5th c.BC+]