dullness vs subduedness

dullness and subduedness both are nouns.

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

As nouns, subduedness is a hyponym of dullness; that is, subduedness is a word with a more specific, narrower meaning than dullness:

dullness: a lack of visual brightness
subduedness: the property of lights or sounds that lack brilliance or are reduced in intensity

Other hyponyms of dullness include dimness, flatness, lusterlessness, lustrelessness, mat, matt, matte.

dullness (noun)	subduedness (noun)
lack of sensibility	the property of lights or sounds that lack brilliance or are reduced in intensity
without sharpness or clearness of edge or point	a disposition to be patient and long suffering
the quality of lacking interestingness
a lack of visual brightness
the quality of being slow to understand