fill in vs crosshatch

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

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

As verbs, crosshatch is a hyponym of fill in; that is, crosshatch is a word with a more specific, narrower meaning than fill in:

fill in (noun)	crosshatch (noun)
	shading consisting of multiple crossing lines

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