dimness vs semidarkness

dimness and semidarkness both are nouns.

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

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

dimness (noun)	semidarkness (noun)
the property of lights or sounds that lack brilliance or are reduced in intensity	partial darkness
the quality of being dim or lacking contrast
the state of being poorly illuminated