moulder vs decay

moulder is not a noun while decay is a noun.

Word	Noun	Adjective	Verb	Adverb
moulder	No	No	Yes	No
decay	Yes	No	Yes	No

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

moulder (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

moulder (verb)	decay (verb)
break down	fall into decay or ruin
	lose a stored charge, magnetic flux, or current
	undergo decay or decomposition