This is the 2837th most frequent French word.
deuil
Mourning or grief after a loss.
Here, "deuil" is used to signify an official state of mourning due to the loss of a notable figure.
Le deuil national a été décrété après le décès du président.
A national mourning was declared after the president's death.
In this case, "deuil" refers to the act of displaying personal grief and mourning through attire.
Elle porte du noir en signe de deuil.
She wears black as a sign of mourning.
Here, "faire son deuil" metaphorically denotes the emotional process of coming to terms with a loss or letting go of attachment.