perspicuity vs lucidness

perspicuity and lucidness both are nouns.

Word	Noun	Adjective	Verb	Adverb
perspicuity	Yes	No	No	No
lucidness	Yes	No	No	No

As nouns, lucidness is a hypernym of perspicuity; that is, lucidness is a word with a broader meaning than perspicuity:

perspicuity: clarity as a consequence of being perspicuous
lucidness: free from obscurity and easy to understand; the comprehensibility of clear expression

Other hypernyms of perspicuity include clarity, clearness, limpidity, lucidity, pellucidity.

perspicuity (noun)	lucidness (noun)
clarity as a consequence of being perspicuous	free from obscurity and easy to understand; the comprehensibility of clear expression