G1596
ἑκουσίως
voluntarily
ἑκουσίως adv., [in LXX: Psa.54:6 (נְדָבָה) 2Ma.14:3, al. ;] voluntarily, willingly: Heb.10:26, 1Pe.5:2.† (AS)
The KJV translates G1596 in the following manner:
wilfully (2x), willingly (2x)
Full Thayer's lexicon entry
ἑκουσίως — hekousíōs
ἑκουσίως, adverb (from Euripides down), voluntarily, willingly, of one's own accord: Heb 10:26 (ἑκουσίως ἁμαρτάνειν (A. V. to sin willfully) is tacitly opposed to sins committed inconsiderately, and from ignorance or from weakness); 1Pe 5:2.
2 occurrences
Hebrews (1), I Peter (1)