opacity vs cloudiness

opacity and cloudiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
opacity	Yes	No	No	No
cloudiness	Yes	No	No	No

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

opacity: the quality of being opaque to a degree; the degree to which something reduces the passage of light
cloudiness: the quality of being cloudy

Other hyponyms of opacity include muddiness, murkiness, blurriness, fogginess, fuzziness, indistinctness, softness.

opacity (noun)	cloudiness (noun)
the quality of being opaque to a degree; the degree to which something reduces the passage of light	the quality of being cloudy
incomprehensibility resulting from obscurity of meaning	the state of the sky when it is covered by clouds
the phenomenon of not permitting the passage of electromagnetic radiation	gloomy semidarkness caused by cloud cover