spit up vs spit out

spit up and spit out both are verbs.

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

As verbs, spit up and spit out are synonyms defined as:

spit up and spit out: discharge (phlegm or sputum) from the lungs and out of the mouth

Other synonyms of spit up include cough out, cough up, expectorate.

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

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

spit up (verb)	spit out (verb)
discharge (phlegm or sputum) from the lungs and out of the mouth	spit up in an explosive manner
give reluctantly	discharge (phlegm or sputum) from the lungs and out of the mouth
	utter with anger or contempt