The Greek adverb hekousios means willingly or voluntarily — acting of one's own free choice without compulsion. Derived from hekōn (willing), it emphasizes the voluntary, self-determined nature of an action and contrasts with compulsion or coercion.
Hekousios appears in two theologically significant passages. Hebrews 10:26: 'If we willingly go on sinning after receiving knowledge of the truth, no sacrifice for sins is left.' This is the apostasy warning: deliberate, persistent, knowing rejection of Christ leaves no further remedy. 1 Peter 5:2 commands elders to shepherd 'not because you must, but because you are willing.' Ministry compelled by obligation bears little fruit; ministry flowing from genuine willingness reflects the character of the Chief Shepherd who gave His life voluntarily (John 10:18).