crisp vs heat up

crisp is a noun but heat up is not a noun.

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

As verbs, heat up is a hypernym of crisp; that is, heat up is a word with a broader meaning than crisp:

Other hypernyms of crisp include heat.

crisp (noun)	heat up (noun)
a thin crisp slice of potato fried in deep fat

crisp (adjective)	heat up (adjective)
pleasantly cold and invigorating
brief and to the point; effectively cut short
(of hair) in small tight curls
(of something seen or heard) clearly defined
pleasingly firm and fresh
tender and brittle

crisp (verb)	heat up (verb)
make brown and crisp by heating	make hot or hotter
make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic	gain heat or get hot
	make more intense