'Mourn' in the Bible

and they mourn, and weep, and fast till the evening, for Saul, and for Jonathan his son, and for the people of Jehovah, and for the house of Israel, because they have fallen by the sword.

And David said to Joab, and to all the people that were with him, Rend your clothes, and gird you with sackcloth, and mourn before Abner. And king David himself followed the bier.

Absalom continued to flee, eventually going to Ammihud's son King Talmai of Geshur, while King David continued to mourn for his son every day.

So Joab sent to Tekoa and took from there a wise woman, and he said to her, "Please pretend to mourn and put on garments of mourning. You should not anoint yourself [with] oil, and you must act like this woman who has been mourning over the dead for {a long time}.

The victory had become an occasion for the army to mourn, because on that very day the troops heard the announcement, "The king is grieving for his son!"