mourning vs bereft

mourning is a noun but bereft is not a noun.

Word	Noun	Adjective	Verb	Adverb
mourning	Yes	Yes	No	No
bereft	No	Yes	No	No

As adjectives, mourning and bereft are synonyms defined as:

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

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

mourning (adjective)	bereft (adjective)
sorrowful through loss or deprivation	sorrowful through loss or deprivation
	unhappy in love; suffering from unrequited love