sustain vs demonstrate

sustain and demonstrate both are verbs.

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

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

sustain: establish or strengthen as with new evidence or facts
demonstrate: establish the validity of something, as by an example, explanation or experiment

Other hyponyms of sustain include back, back up, vouch, verify, establish, prove, shew, show, document, validate.

sustain (verb)	demonstrate (verb)
undergo (as of injuries and illnesses)	establish the validity of something, as by an example, explanation or experiment
establish or strengthen as with new evidence or facts	provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes
admit as valid	give an exhibition of to an interested audience
supply with necessities and support	march in protest; take part in a demonstration
provide with nourishment
be the physical support of; carry the weight of
lengthen or extend in duration or space