fill in vs art

fill in is not a noun while art is a noun.

Word	Noun	Adjective	Verb	Adverb
fill in	No	No	Yes	No
art	Yes	No	No	No

fill in (noun)	art (noun)
	the creation of beautiful or significant things
	the products of human creativity; works of art collectively
	a superior skill that you can learn by study and practice and observation
	photographs or other visual representations in a printed publication

fill in (verb)	art (verb)
supply with information on a specific topic
write all the required information onto a form
represent the effect of shade or shadow on
be a substitute