obscureness vs semidarkness

obscureness and semidarkness both are nouns.

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

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

obscureness: the state of being indistinct or indefinite for lack of adequate illumination
semidarkness: partial darkness

obscureness (noun)	semidarkness (noun)
the quality of being unclear or abstruse and hard to understand	partial darkness
the state of being humble and unimportant
the state of being indistinct or indefinite for lack of adequate illumination