rudeness vs rude

rudeness is a noun but rude is not a noun.

Word	Noun	Adjective	Verb	Adverb
rudeness	Yes	No	No	No
rude	No	Yes	No	No

rudeness (noun)	rude (noun)
a manner that is rude and insulting
a wild or unrefined state

rudeness (adjective)	rude (adjective)
	lacking civility or good manners
	belonging to an early stage of technical development; characterized by simplicity and (often) crudeness
	socially incorrect in behavior
	(used especially of commodities) being unprocessed or manufactured using only simple or minimal processes
	(of persons) lacking in refinement or grace