somberness vs apprehension

somberness and apprehension both are nouns.

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

As nouns, apprehension is a hypernym of somberness; that is, apprehension is a word with a broader meaning than somberness:

Other hypernyms of somberness include apprehensiveness, dread, melancholy.

somberness (noun)	apprehension (noun)
a manner that is serious and solemn	the act of apprehending (especially apprehending a criminal)
a feeling of melancholy apprehension	the cognitive condition of someone who understands
a state of partial or total darkness	painful expectation
	fearful expectation or anticipation