heat up vs broil

heat up is not a noun while broil is a noun.

Word	Noun	Adjective	Verb	Adverb
heat up	No	No	Yes	No
broil	Yes	No	Yes	No

As verbs, broil is a hyponym of heat up; that is, broil is a word with a more specific, narrower meaning than heat up:

Other hyponyms of heat up include crisp, crispen, toast, scald, soak, calcine, preheat, overheat, scorch, sear, bake, reheat.

heat up (noun)	broil (noun)
	cooking by direct exposure to radiant heat (as over a fire or under a grill)

heat up (verb)	broil (verb)
make hot or hotter	cook under a broiler
gain heat or get hot	heat by a natural force
make more intense	be very hot, due to hot weather or exposure to the sun