opaqueness vs fogginess

opaqueness and fogginess both are nouns.

Word	Noun	Adjective	Verb	Adverb
opaqueness	Yes	No	No	No
fogginess	Yes	No	No	No

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

opaqueness: the quality of being opaque to a degree; the degree to which something reduces the passage of light
fogginess: the quality of being indistinct and without sharp outlines

Other hyponyms of opaqueness include cloudiness, muddiness, murkiness, blurriness, fuzziness, indistinctness, softness.

opaqueness (noun)	fogginess (noun)
the quality of being opaque to a degree; the degree to which something reduces the passage of light	the quality of being indistinct and without sharp outlines
incomprehensibility resulting from obscurity of meaning	an atmosphere in which visibility is reduced because of a cloud of some substance