somberness vs graveness

somberness and graveness both are nouns.

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

As nouns, somberness and graveness are synonyms defined as:

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

somberness (noun)	graveness (noun)
a manner that is serious and solemn	a manner that is serious and solemn
a feeling of melancholy apprehension
a state of partial or total darkness