sobriety vs seriousness

sobriety and seriousness both are nouns.

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

As nouns, seriousness is a hypernym of sobriety; that is, seriousness is a word with a broader meaning than sobriety:

Other hypernyms of sobriety include earnestness, serious-mindedness, sincerity.

sobriety (noun)	seriousness (noun)
abstaining from excess	the trait of being serious
a manner that is serious and solemn	the quality of arousing fear or distress
moderation in or abstinence from alcohol or other drugs	an earnest and sincere feeling
the state of being sober and not intoxicated by alcohol