sombreness vs graveness

sombreness and graveness both are nouns.

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

As nouns, sombreness and graveness are synonyms defined as:

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

sombreness (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