restraint vs plainness

restraint and plainness both are nouns.

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

As nouns, plainness is a hypernym of restraint; that is, plainness is a word with a broader meaning than restraint:

restraint (noun)	plainness (noun)
the act of controlling by restraining someone or something	the appearance of being plain and unpretentious
a device that retards something's motion	an appearance that is not attractive or beautiful
discipline in personal and social activities	clarity as a consequence of being perspicuous
lack of ornamentation	the state of being unmixed with other material
a rule or condition that limits freedom
the state of being physically constrained