The Greek adjective adikos (ἄδικος) is composed of the alpha-privative (a-, not) and dikaios (G1342, just/righteous). It means unjust, unrighteous, wicked, or dishonest — the opposite of the central Greek-biblical virtue of righteousness.
Adikos appears in Jesus's parable of the Dishonest Manager (Luke 16:10-11), where Jesus paradoxically commends shrewd use of 'unrighteous wealth' (mamona tou adikiou) for kingdom purposes. Paul uses the word in 1 Corinthians 6:9: 'the unrighteous (adikoi) will not inherit the kingdom of God.' The contrast between the dikaios (righteous) and adikos (unrighteous) runs throughout Scripture, culminating in God's perfect justice at the last day. Yet 1 Peter 3:18 offers the gospel's great reversal: Christ died 'the just for the unjust' (dikaios hyper adikon).