exchange vs fill in

exchange is a noun but fill in is not a noun.

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

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

Other hyponyms of exchange include sell, cash, cash in, ransom, redeem, redeem, stand in, sub, substitute, swap, switch, swop, trade, barter, trade, trade in.

exchange (noun)	fill in (noun)
reciprocal transfer of equivalent sums of money (especially the currencies of different countries)
the act of putting one thing or person in the place of another:
the act of changing one thing for another thing
the act of giving something in return for something received
(chess) the capture by both players (usually on consecutive moves) of pieces of equal value
(chess) gaining (or losing) a rook in return for a knight or bishop
(sports) an unbroken sequence of several successive strokes
a workplace for buying and selling; open only to members
a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication
a mutual expression of views (especially an unpleasant one)
chemical process in which one atom or ion or group changes places with another

exchange (verb)	fill in (verb)
exchange or replace with another, usually of the same kind or category	supply with information on a specific topic
change over, change around, as to a new order or sequence	write all the required information onto a form
exchange a penalty for a less severe one	represent the effect of shade or shadow on
give to, and receive from, one another	be a substitute
put in the place of another; switch seemingly equivalent items
hand over one and receive another, approximately equivalent