trip up vs stumble

trip up is not a noun while stumble is a noun.

Word	Noun	Adjective	Verb	Adverb
trip up	No	No	Yes	No
stumble	Yes	No	Yes	No

As verbs, trip up and stumble are synonyms defined as:

Other synonyms of trip up include slip up.

trip up (noun)	stumble (noun)
	an unsteady uneven gait
	an unintentional but embarrassing blunder

trip up (verb)	stumble (verb)
detect a blunder or misstep	make an error
make an error	miss a step and fall or nearly fall
cause to stumble	walk unsteadily, tripping repeatedly
	encounter by chance