This verb means to act treacherously or deal deceitfully with someone. Romans 3:13 quotes Psalm 5:9 in Paul's catalog of universal human sinfulness: 'they kept deceiving with their tongues.' The term emphasizes ongoing deceptive behavior and treacherous dealing. The Septuagint uses it for acting with guile or betraying trust. Classical Greek similarly employed it for treacherous conduct. Paul's use highlights the moral corruption of humanity—speech itself becomes an instrument of deception and betrayal.