mix up vs stump

mix up is not a noun while stump is a noun.

Word	Noun	Adjective	Verb	Adverb
mix up	No	No	Yes	No
stump	Yes	No	Yes	No

As verbs, mix up and stump are synonyms defined as:

mix up (noun)	stump (noun)
	(cricket) any of three upright wooden posts that form the wicket
	a platform raised above the surrounding level to give prominence to the person on it
	the part of a limb or tooth that remains after the rest is removed
	the base part of a tree that remains standing after the tree has been felled

mix up (verb)	stump (verb)
cause to be perplexed or confounded	remove tree stumps from
assemble without order or sense	cause to be perplexed or confounded
	travel through a district and make political speeches
	walk heavily