fill out vs modify

fill out and modify both are verbs.

Word	Noun	Adjective	Verb	Adverb
fill out	No	No	Yes	No
modify	No	No	Yes	No

As verbs, modify is a hypernym of fill out; that is, modify is a word with a broader meaning than fill out:

Other hypernyms of fill out include alter, change.

fill out (verb)	modify (verb)
become round, plump, or shapely	make less severe or harsh or extreme
make bigger or better or more complete	add a modifier to a constituent
write all the required information onto a form	cause to change; make different; cause a transformation
make fat or plump
line or stuff with soft material
supplement what is thought to be deficient