formal vs informal

formal is a noun but informal is not a noun.

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

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

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