insipidness vs dullness

insipidness and dullness both are nouns.

Word	Noun	Adjective	Verb	Adverb
insipidness	Yes	No	No	No
dullness	Yes	No	No	No

As nouns, dullness is a hypernym of insipidness; that is, dullness is a word with a broader meaning than insipidness:

insipidness (noun)	dullness (noun)
lacking any distinctive or interesting taste property	lack of sensibility
extreme dullness; lacking spirit or interest	without sharpness or clearness of edge or point
	the quality of lacking interestingness
	a lack of visual brightness
	the quality of being slow to understand