“opponent.” The Greek word is antidikos (#476 ἀντίδικος), and it has two meanings: to be constantly against as an enemy to, or to be an opponent in a court of law (thus, an “opponent at law”). The word antidikos occurs five times in the New Testament, and here in Matthew it has the legal meaning of an opponent in a lawsuit (cp. NASB in Matt. 5:25). The other occurrences seem to fit the general situation of an opponent well (see commentary on 1 Pet. 5:8).