Adikōs (G95) is the adverb from adikos (unjust, G94), meaning to act in a way that is contrary to right (dikaios). It occurs once in the NT (1 Peter 2:19) in the context of suffering unjustly — bearing pain for doing good, as Christ did.
Peter's use of adikōs elevates unjust suffering as a participation in Christ's passion. To suffer wrongfully and endure it patiently is a witness to the gospel. Jesus suffered adikōs supremely — condemned by false testimony, executed as innocent. His unjust death becomes the just foundation of our justification.