sustain vs shore up

sustain and shore up both are verbs.

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

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

Other hyponyms of sustain include scaffold, block, carry, chock, buoy, buoy up, pole, bracket, underpin, prop, prop up, shore, truss, brace.

sustain (verb)	shore up (verb)
undergo (as of injuries and illnesses)	support by placing against something solid or rigid
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