prop up vs sustain

prop up and sustain both are verbs.

Word	Noun	Adjective	Verb	Adverb
prop up	No	No	Yes	No
sustain	No	No	Yes	No

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

Other hypernyms of prop up include hold, hold up, support.

prop up (verb)	sustain (verb)
support by placing against something solid or rigid	undergo (as of injuries and illnesses)
	establish or strengthen as with new evidence or facts
	admit as valid
	supply with necessities and support
	provide with nourishment
	be the physical support of; carry the weight of
	lengthen or extend in duration or space