underpin vs sustain

underpin and sustain both are verbs.

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

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

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

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