plainness vs perspicuity

plainness and perspicuity both are nouns.

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

As nouns, plainness and perspicuity are synonyms defined as:

plainness and perspicuity: clarity as a consequence of being perspicuous

Other synonyms of plainness include perspicuousness.

plainness (noun)	perspicuity (noun)
the appearance of being plain and unpretentious	clarity as a consequence of being perspicuous
an appearance that is not attractive or beautiful
clarity as a consequence of being perspicuous
the state of being unmixed with other material