slip up vs stumble

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

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

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

Other synonyms of slip up include trip up.

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

slip up (verb)	stumble (verb)
make an error	make an error
	miss a step and fall or nearly fall
	walk unsteadily, tripping repeatedly
	encounter by chance