Atonement is the act — or the making-peace itself — that shows you are sorry and tries to repair a wrong. It can be a human thing (a hard apology, paying someone back, years of quieter living) or a religious idea. In Christianity, the Atonement (often with a capital A) is the teaching that Jesus's death puts people right with God; that use is church language, not everyday chat. In ordinary English the word is serious and a little formal. Book and film titles like Atonement use it for guilt that will not sit still, and for the long work of trying to make it right. Though actually, atonement is not always a finished job you can tick off; sometimes the word is about the effort, not a clean ending.