sustain vs underpin

sustain and underpin both are verbs.

Word	Noun	Adjective	Verb	Adverb
sustain	No	No	Yes	No
underpin	No	No	Yes	No

As verbs, underpin is a hyponym of sustain; that is, underpin 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, prop, prop up, shore, shore up, truss, brace.

sustain (verb)	underpin (verb)
undergo (as of injuries and illnesses)	support from beneath
establish or strengthen as with new evidence or facts	support with evidence or authority or make more certain or confirm
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