come up vs muster up

come up and muster up both are verbs.

Word	Noun	Adjective	Verb	Adverb
come up	No	No	Yes	No
muster up	No	No	Yes	No

As verbs, come up and muster up are synonyms defined as:

Other synonyms of come up include muster, rally, summon.

come up (verb)	muster up (verb)
result or issue	gather or bring together
start running, functioning, or operating
gather or bring together
gather (money or other resources) together over time
bring forth, usually something desirable
come up, of celestial bodies
come to the surface
move toward, travel toward something or somebody or approach something or somebody
move upward
get something or somebody for a specific purpose
originate or come into being
be mentioned