informal vs common

informal is not a noun while common is a noun.

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

informal (noun)	common (noun)
	a piece of open land for recreational use in an urban area

informal (adjective)	common (adjective)
not formal	having no special distinction or quality; widely known or commonly encountered; average or ordinary or usual
used of spoken and written language	belonging to or participated in by a community as a whole; public
having or fostering a warm or friendly and informal atmosphere	commonly encountered
not officially recognized or controlled	of low or inferior quality or value
	being or characteristic of or appropriate to everyday language
	of or associated with the great masses of people
	to be expected; standard
	common to or shared by two or more parties
	lacking refinement or cultivation or taste