The Greek katalalos (G2637) means a slanderer or backbiter — one who speaks behind another's back to injure them. It appears in Romans 1:30, in the catalog of the morally degraded: 'gossips, slanderers (katalaloi), God-haters.' The related verb katalaleo appears in James 4:11: 'Brothers and sisters, do not slander (katalaleo) one another.' The prefix kata suggests speaking down against someone — the act of diminishing another through speech.
Katalalos in Romans 1:30 appears in a list that begins with cosmic rebellion against God and ends with slanderers and parent-haters — the social symptoms of a society that has exchanged God's glory for idols. Slander is not merely impolite; it is spiritually diagnostic. It reveals a heart shaped by the accuser (diabolos — devil — means 'the accuser'). James 4:11-12 goes further: 'Anyone who speaks against a brother or sister or judges them speaks against the law and judges it... There is only one Lawgiver and Judge.' To slander a person made in God's image is to indict God's work.