shadowiness vs semidarkness

shadowiness and semidarkness both are nouns.

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

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

shadowiness: relative darkness caused by light rays being intercepted by an opaque body
semidarkness: partial darkness

shadowiness (noun)	semidarkness (noun)
relative darkness caused by light rays being intercepted by an opaque body	partial darkness