grief-stricken vs mourning

grief-stricken is not a noun while mourning is a noun.

Word	Noun	Adjective	Verb	Adverb
grief-stricken	No	Yes	No	No
mourning	Yes	Yes	No	No

As adjectives, grief-stricken and mourning are synonyms defined as:

Other synonyms of grief-stricken include bereaved, bereft, grieving, sorrowing.

grief-stricken (noun)	mourning (noun)
	the passionate and demonstrative activity of expressing grief
	state of sorrow over the death or departure of a loved one

grief-stricken (adjective)	mourning (adjective)
sorrowful through loss or deprivation	sorrowful through loss or deprivation