mourn [intransitive and transitive]
to feel very sad and to miss someone after they have died [= grieve for]:
Hundreds of people gathered to mourn the slain president.
They mourned for their children, killed in the war.
mourn somebody's death/loss/passing
She still mourns the death of her husband.
to feel very sad because something no longer exists or is no longer as good as it used to be:
The old steam trains were much-loved, and we all mourn their passing.