sustain vs buoy

sustain is not a noun while buoy is a noun.

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

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

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

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

sustain (verb)	buoy (verb)
undergo (as of injuries and illnesses)	mark with a buoy
establish or strengthen as with new evidence or facts	keep afloat
admit as valid	float on the surface of water
supply with necessities and support
provide with nourishment
be the physical support of; carry the weight of
lengthen or extend in duration or space