Both πονηρός and φαῦλοςare translated 'evil,' but their application in scripture is different, though they may seem to blend. φαῦλος occurs but four times, referring to doing evil, John 3:20; John 5:29; and to the character of what is done as being evil. Titus 2:8; James 3:16 .
πονηρός(from πόηος, 'labour, sorrow') often refers to the evil nature of the one acting, and the active working out of it. Thus Satan is called that 'wicked' one. Matthew 13:19,38; Ephesians 6:16; 1 John 2:13,14; 1 John 3:12 . The demons are evil spirits. Luke 7:21; Luke 8:2; Acts 19:12-16 . The same word is used in reference to the man living in sin in the church at Corinth — "put away . . . . that wicked person." 1 Corinthians 5:13 .
κακός, with its many compounds, is a common word for evil and (like πονηρός) may apply to the nature or character of those who commit evil. Matthew 21:41; Matthew 24:48; Philippians 3:2; Revelation 2:2; as well as to their acts and principles, Mark 7:21; 1 Corinthians 15:33; Colossians 3:5; Romans 1:30; Romans 8:3; 2 Corinthians 13:7; though not always with this moral force: see Acts 16:28; Acts 28:5; 'harm'; and Luke 16:25 , 'evil things.'
πονηρός would in Latin be industriâ malus, malignus. So the enemy of souls is emphatically, ὁ πονηρός, "the evil one." κακός in Latin is malus, improbus , etc., and is used in a very general way, opposed to both καλός and ἀγαθός, 'good:' 3 John 11 . Both κακός and πονηρός occur in Revelation 16:2; "noisome (κα.) and grievous (πο.)"; and their nouns κακία and πονηρία, "malice and wickedness." 1 Corinthians 5:8 .