decay vs wear away

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

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

As verbs, wear away is a hyponym of decay; that is, wear away is a word with a more specific, narrower meaning than decay:

decay (noun)	wear away (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

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