spit up vs sputter

spit up is not a noun while sputter is a noun.

Word	Noun	Adjective	Verb	Adverb
spit up	No	No	Yes	No
sputter	Yes	No	Yes	No

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

Other hyponyms of spit up include cough, ptyalise, ptyalize, spew, spit, spue, spit out, splutter.

spit up (noun)	sputter (noun)
	an utterance (of words) with spitting sounds (as in rage)
	the noise of something spattering or sputtering explosively

spit up (verb)	sputter (verb)
discharge (phlegm or sputum) from the lungs and out of the mouth	spit up in an explosive manner
give reluctantly	cause to undergo a process in which atoms are removed
	utter with a spitting sound, as if in a rage
	climb awkwardly, as if by scrambling
	make an explosive sound