Isn't that a beautiful word?
This is the definition, as provided by the lovely dictionary.com:
piacular \pahy-AK-yuh-ler\ , adjective:
1. Expiatory; atoning; reparatory.
2. Requiring expiation; sinful or wicked.
The word Piacular is derived from two Latin roots: pia, which is related to the word pious, and a variation of the suffix -cule which denotes a diminutive noun, like particle.
So now your goal is to use this word in a sentence. How about this?
Alicia knew her action merited a piacular action if Lanthian was ever to forgive her.
Now, just to make things interesting use that sentence in a book you are writing.
Fun? I KNOW!