wear away vs decay

wear away is not a noun while decay is a noun.

Word	Noun	Adjective	Verb	Adverb
wear away	No	No	Yes	No
decay	Yes	No	Yes	No

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

Other hypernyms of wear away include crumble, dilapidate.

wear away (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

wear away (verb)	decay (verb)
become ground down or deteriorate	fall into decay or ruin
diminish, as by friction	lose a stored charge, magnetic flux, or current
cut away in small pieces	undergo decay or decomposition