footnote vs write

footnote is a noun but write is not a noun.

Word	Noun	Adjective	Verb	Adverb
footnote	Yes	No	Yes	No
write	No	No	Yes	No

As verbs, write is a hypernym of footnote; that is, write is a word with a broader meaning than footnote:

Other hypernyms of footnote include compose, indite, pen.

footnote (noun)	write (noun)
a printed note placed below the text on a printed page

footnote (verb)	write (verb)
add explanatory notes to or supply with critical comments	communicate or express by writing
	record data on a computer
	contact in writing
	produce a literary work
	mark or trace words or symbols on a surface
	write or name the letters that comprise the conventionally accepted form of (a word or part of a word)
	write music
	create code, write a computer program