الْوَسْوَاسِ (whisperer): The one who adorns evil deeds in your ears.

الْخَنَّاسِ (retreating): Going back and lag behind, since he retreats and goes back when Allah (swt) is remembered.

Allah (swt) named Satan as (retreating whisperer) because he usually whispers to people but he retreats and disappears when Allah (swt) is mentioned, if not, Satan takes the chance to be entirely with the man who is far away from his Lord.