Nouns

(n)plainnessthe state of being unmixed with other material“the plainness of vanilla ice cream”
(n)perspicuity, perspicuousness, plainnessclarity as a consequence of being perspicuous
(n)plainnessthe appearance of being plain and unpretentious
(n)homeliness, plainnessan appearance that is not attractive or beautiful“fine clothes could not conceal the girl's homeliness”