fill vs feed upon

fill is a noun but feed upon is not a noun.

Word	Noun	Adjective	Verb	Adverb
fill	Yes	No	Yes	No
feed upon	No	No	Yes	No

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

fill (noun)	feed upon (noun)
a quantity sufficient to satisfy
any material that fills a space or container

fill (verb)	feed upon (verb)
become full	be sustained by
make full, also in a metaphorical sense
plug with a substance
fill to satisfaction
eat until one is sated
fill, satisfy or meet a want or need or condition or restriction
assume, as of positions or roles
appoint someone to (a position or a job)
occupy the whole of