sobriety vs somberness

sobriety and somberness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sobriety	Yes	No	No	No
somberness	Yes	No	No	No

As nouns, sobriety and somberness are synonyms defined as:

Other synonyms of sobriety include graveness, gravity, soberness, sombreness.

sobriety (noun)	somberness (noun)
abstaining from excess	a manner that is serious and solemn
a manner that is serious and solemn	a feeling of melancholy apprehension
moderation in or abstinence from alcohol or other drugs	a state of partial or total darkness
the state of being sober and not intoxicated by alcohol