plainness vs perspicuousness

plainness and perspicuousness both are nouns.

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

As nouns, plainness and perspicuousness are synonyms defined as:

plainness and perspicuousness: clarity as a consequence of being perspicuous

Other synonyms of plainness include perspicuity.

plainness (noun)	perspicuousness (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