patch up vs mend

patch up is not a noun while mend is a noun.

Word	Noun	Adjective	Verb	Adverb
patch up	No	No	Yes	No
mend	Yes	No	Yes	No

As verbs, mend is a hypernym of patch up; that is, mend is a word with a broader meaning than patch up:

patch up: mend by putting a patch on
mend: restore by replacing a part or putting together what is torn or broken

Other hypernyms of patch up include bushel, doctor, fix, furbish up, repair, restore, touch on.

patch up (noun)	mend (noun)
	the act of putting something in working order again
	sewing that repairs a worn or torn hole (especially in a garment)

patch up (verb)	mend (verb)
mend by putting a patch on	restore by replacing a part or putting together what is torn or broken
come to terms	heal or recover