Rebecca has a post looking at the word propitiation, its usage and a challenge to figure out another word that can fit in its place. Unfortunately (or fortunately depending on your bend in modern bible translations) I’m all for the actual word propitiation but I also readily admit that there might be a shift of usage depending on the Biblical author. Paul might be making an allusion to the OT mercy seat and John may be referring to what the mercy seat offering accomplished in a general sense. So whereas Paul might be saying "God publicly (instead of behind a veil) revealed the place where God’s wrath was turned away and satisfied in the person of His Son on the cross" John would be saying "Jesus Christ is the atoning sacrifice for the world, but for us believers especially."
Be that as it may, I’ll play and try to update (if not dumb down) the actual word.
Some suggestions have already been offered like: expiation, wrath payment, wrath-remover and others. Personally I think these words have a theological roughness around the edges when read by a modern reader since they imply things today that they wouldn’t have yesteryear. For instance, wrath is has a different meaning today than what the Bible says—meaning more revenge, usually by someone with too much self-importance. So I would have to replace that with something like "justified fury" (since we use both terms today often enough and Anger is too soft and Rage sounds out of control).
Maybe "an appeasement of justified fury" but then that just seems to highlight one aspect of it while ignoring the mercy seat/atoning aspect where the sacrifice was not only allowing God to bear the people’s sinful presence but also allowed them to serve him in worship. There’s a sense where it’s definitely more than satisfaction/diverting of justified fury but includes a blanket covering that allows actual peace (unlike the "peace" of the Cold War—but real, same-side-of-the-table peace!).
In the end how about "an appeasing atonement for justified fury" but then, atonement isn’t commonly used? So, instead of that, how about "an appeasing forgiveness-inducing offering for justified fury".
If I try it on it’ll read something like: God publicly displayed an appeasing forgiveness-inducing offering for justified fury for entire world to see, which is Christ Jesus, and is especially applicable to us. I might be able to walk around in it a bit, but offering feels a bit too tight for modern shoes so in the end I’ll probably just go back to my good ol’ trusty Propitiatory/Propitiation and explain with an OT object lesson.
(I cross posted this on Rebecca’s site, but edited it a bit to read more like a post and clear up some things I accidentally typed sans-thinking. I also rewrote this for my personal blog to see if I can say the same things in regular English to a different audience.)