Righteous, just, conforming to God's standard. Dikaios describes one who is in right standing — either through personal conduct or through God's declaration. It is the adjective form of dikaiosynē (righteousness), the central concept in Paul's theology of justification.
The NT tension: 'There is no one righteous, not even one' (Romans 3:10), yet God 'justifies the ungodly' (Romans 4:5). How can the unrighteous become dikaios? Paul's answer: through faith in Christ, God declares sinners righteous — imputing Christ's righteousness to them. Jesus is 'the Righteous One' (Acts 3:14) who makes the unrighteous right. It's forensic language — a legal verdict of acquittal.