mourning

mourn‧ing /ˈmɔːnɪŋ $ ˈmɔːr-/ BrE AmE noun [uncountable]
1. great sadness because someone has died:
The Armenian authorities declared May 29 a national day of mourning.
in mourning (=feeling great sadness)
It was the custom to visit those in mourning and sit quietly with them.
2. black clothes worn to show that you are very sad that someone has died:
She was recently widowed and wearing mourning.

Oxford Advanced Learner's Dictionary

mourning

mourn·ing [mourning] [ˈmɔːnɪŋ] [ˈmɔːrnɪŋ] noun uncountable
1. sadness that you show and feel because sb has died
Syn: grief
• The government announced a day of national mourning for the victims.

• She was still in mourning for her husband.

2. clothes that people wear to show their sadness at sb's death
• The queen was dressed in mourning.
Example Bank:
• She was still in full mourning six months after her son's death.
• a day of mourning for the victims of the tragedy

• The government has announced a day of national mourning for the victims.

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

mourning / ˈmɔː.nɪŋ / / ˈmɔːr- / noun [ U ]

great sadness felt because someone has died:

Shops will be closed today as a sign of mourning for the king.

He was in mourning for his wife.

the usually black clothes that are worn in some countries as an expression of sadness about someone's death a loud crying that people in some countries make when someone dies:

The mourning could be heard all day and all night.

Collins Advanced Learner’s English Dictionary

mourning

[mɔ͟ː(r)nɪŋ]
1) N-UNCOUNT Mourning is behaviour in which you show sadness about a person's death.
  The period of mourning and bereavement may be long...
  Expect to feel angry, depressed and confused. It's all part of the mourning process...
  Human rights groups declared what they called a day of mourning and protest.
2) PHRASE: usu v-link PHR If you are in mourning, you are dressed or behaving in a particular way because someone you love or respect has died.
  Yesterday the whole of Greece was in mourning...
  The boys wore black tail coats in mourning for George III.

Merriam-Webster's Advanced Learner's Dictionary

mourning

mourn·ing /ˈmoɚnɪŋ/ noun [noncount]
1 : the act of mourning for someone who has died
• a day of national mourning
• She is still in mourning for her dead husband.
• The whole town was in mourning.
• She went into mourning for her dead husband. [=she began to mourn for her dead husband]
2 : great sadness felt because someone has died
• a period of deep mourning
3 : black clothing that is worn to show that you are mourning for someone who has died
• His widow was dressed in mourning.