fatten up vs feed

fatten up is not a noun while feed is a noun.

Word	Noun	Adjective	Verb	Adverb
fatten up	No	No	Yes	No
feed	Yes	No	Yes	No

fatten up (noun)	feed (noun)
	food for domestic livestock

fatten up (verb)	feed (verb)
make fat or plump	provide with fertilizers or add nutrients to
	introduce continuously
	take in food; used of animals only
	give food to
	serve as food for; be the food for
	feed into; supply
	provide as food
	gratify
	profit from in an exploitatory manner
	move along, of liquids
	support or promote