Noun and する verb
ちんこん
星祭りは、平和を祈り、戦死者を鎮魂する儀式です。
Tanabata is a ritual to pray for peace and give repose to people killed in the war.
To tranquilize souls you have to a have a mass repose of souls. Then their souls will move on to the next life and stop hanging around here, haunting umbrellas.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.