sorrow vs mourning

sorrow and mourning both are nouns.

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

As nouns, mourning is a hyponym of sorrow; that is, mourning is a word with a more specific, narrower meaning than sorrow:

Other hyponyms of sorrow include bereavement, poignance, poignancy.

sorrow (noun)	mourning (noun)
something that causes great unhappiness	the passionate and demonstrative activity of expressing grief
an emotion of great sadness associated with loss or bereavement	state of sorrow over the death or departure of a loved one
sadness associated with some wrong done or some disappointment
the state of being sad

sorrow (adjective)	mourning (adjective)
	sorrowful through loss or deprivation

sorrow (verb)	mourning (verb)
feel grief