The Greek noun antidikos (ἀντίδικος) means an adversary or opponent — particularly in a legal setting. It combines anti (against) and dike (justice, lawsuit). It appears five times in the New Testament (Matthew 5:25; Luke 12:58; 18:3; 1 Peter 5:8) and is the word Peter uses for the devil.
The most dramatic use of antidikos is in 1 Peter 5:8: "Your adversary the devil prowls around like a roaring lion, seeking someone to devour." The legal resonance is intentional — the devil is the accuser (Hebrew: satan), our opponent in the courtroom of God's justice (cf. Zechariah 3:1–2; Revelation 12:10). But Jesus is our Advocate (parakletos, 1 John 2:1). The legal imagery runs throughout the New Testament: condemnation vs. justification, accusation vs. intercession. In Luke 18:3, the persistent widow demands justice against her antidikos — Jesus uses it to teach bold, persistent prayer to the Judge who will vindicate His people. Prayer is not passive waiting but active engagement with the God who rules the court.