American Heritage® Dictionary of the English Language, Fifth Edition.
Copyright © 2011 by Houghton Mifflin Harcourt Publishing Company.

Satisfaction or turning away God’s anger against sin 

— Glossary, Luther's Small Catechism with Explanation, 2017 ed., p. 397

1 John 2:1-2 (Literal)
(1) My little children, I write these things to you so that you do not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous.
(2) And He Himself is the propitiation (prō-pĭsh′ē-ā′shən) relating to our sins, and not relating to ours only, but also relating to all the world.