gnaw at vs decay

gnaw at is not a noun while decay is a noun.

Word	Noun	Adjective	Verb	Adverb
gnaw at	No	No	Yes	No
decay	Yes	No	Yes	No

As verbs, decay is a hypernym of gnaw at; that is, decay is a word with a broader meaning than gnaw at:

Other hypernyms of gnaw at include crumble, dilapidate.

gnaw at (noun)	decay (noun)
	the organic phenomenon of rotting
	a gradual decrease; as of stored charge or current
	the process of gradually becoming inferior
	the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
	an inferior state resulting from the process of decaying

gnaw at (verb)	decay (verb)
become ground down or deteriorate	fall into decay or ruin
	lose a stored charge, magnetic flux, or current
	undergo decay or decomposition