“Wicked One.” The Greek is poneros (#4190 πονηρός), which the BDAG Greek-English Lexicon describes as, “pertaining to being morally or socially worthless; therefore, ‘wicked, evil, bad, base, worthless, vicious, and degenerate.’” Poneros is an adjective, but it is a substantive (an adjective used as a noun; for more on substantives, see the commentary on Matthew 5:37).
The Devil (the “Slanderer”) is the fount and foundation of wickedness. It was in him that wickedness was first found, when he was lifted up with pride and decided to rebel against God. Ever since that time he has been true to his name, “the Wicked One,” and has been doing and causing wickedness wherever he can, which, since he is “the god of this age,” is a considerable amount of wickedness. [For more names of the Slanderer (the Devil) and their meanings, see Appendix 14: “Names of the Devil”].