stumble vs trip up

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

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

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

Other synonyms of stumble include slip up.

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

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