to feel and show sadness because somebody has died; to feel sad because something no longer exists or is no longer the same Please, leave us to mourn in peace. mourn something He was still mourning his brother's death. They mourn the passing of a simpler way of life. The city was mourning the victims of the bombings. mourn (for somebody/something) Today we mourn for all those who died in two world wars. She mourned for her lost childhood.