buoy vs sustain

buoy is a noun but sustain is not a noun.

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

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

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

buoy (noun)	sustain (noun)
a float attached by rope to the seabed to mark channels in a harbor or underwater hazards; typically brightly-coloured

buoy (verb)	sustain (verb)
mark with a buoy	undergo (as of injuries and illnesses)
keep afloat	establish or strengthen as with new evidence or facts
float on the surface of water	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