informal vs formal

informal is not a noun while formal is a noun.

Word	Noun	Adjective	Verb	Adverb
informal	No	Yes	No	No
formal	Yes	Yes	No	No

informal (noun)	formal (noun)
	a gown for evening wear
	a lavish dance requiring formal attire

informal (adjective)	formal (adjective)
not formal	being in accord with established forms and conventions and requirements (as e.g. of formal dress)
used of spoken and written language	(of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms
having or fostering a warm or friendly and informal atmosphere	refined or imposing in manner or appearance; befitting a royal court
not officially recognized or controlled	logically deductive
	represented in simplified or symbolic form
	characteristic of or befitting a person in authority