verb/lɛ.se tʁɑ̃.kil/
to leave alone, to leave in peace, to leave be
“Pourquoi est-ce que je me suis attendu à ce que vous ayez la gentillesse de me laisser tranquille ?” — Why did I ever expect that you would be kind enough to leave me alone?
Synonyms: laisser en paix, foutre la paix, lâcher la grappe
Literally, “to leave calm”.