This adjective characterizes those who are morally pure and without guile. In Romans 16:18, Paul warns that deceivers target the ἄκακοι—the innocent and unsuspecting—with smooth talk. Hebrews 7:26 applies it to Christ as our high priest, emphasizing his complete moral purity and separation from sinners. The classical Greek background includes meanings of both "guileless" (unknowing of evil) and "harmless" (doing no evil), reflecting inner purity that makes one vulnerable to deception.