stand firm vs stand up

stand firm and stand up both are verbs.

Word	Noun	Adjective	Verb	Adverb
stand firm	No	No	Yes	No
stand up	No	No	Yes	No

As verbs, stand up is a hyponym of stand firm; that is, stand up is a word with a more specific, narrower meaning than stand firm:

Other hyponyms of stand firm include stand out, outbrave, hold off, remain firm, stand, defy, hold, hold up, withstand.

stand firm (verb)	stand up (verb)
refuse to abandon one's opinion or belief	defend against attack or criticism
stand up or offer resistance to somebody or something	refuse to back down; remain solid under criticism or attack
	be standing; be upright
	put into an upright position
	rise to one's feet
	rise up as in fear
	resist or withstand wear, criticism, etc.