cloudiness vs opacity

cloudiness and opacity both are nouns.

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

As nouns, opacity is a hypernym of cloudiness; that is, opacity is a word with a broader meaning than cloudiness:

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

Other hypernyms of cloudiness include opaqueness.

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