Not To Be Confused With
Propitiation appeases wrath (Godward); expiation removes guilt or cleanses sin (sinward). The same Greek word-group (hilastērion) carries both, and the New Testament includes both — debates turn on whether wrath may be named.
Some translations prefer “expiation” (covering/removing sin) to avoid the idea of placating an angry deity; defenders of “propitiation” answer that Scripture really does speak of God's wrath against sin (Rom 1:18) — wrath turned aside not by us but by God's own provision, the cross. It is God propitiating God.