cloudiness vs semidarkness

cloudiness and semidarkness both are nouns.

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

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

cloudiness (noun)	semidarkness (noun)
the quality of being cloudy	partial darkness
the state of the sky when it is covered by clouds
gloomy semidarkness caused by cloud cover