ruin vs decay

ruin and decay both are nouns.

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

As nouns, decay is a hypernym of ruin; that is, decay is a word with a broader meaning than ruin:

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

Other hypernyms of ruin include crumble, dilapidate.

ruin (noun)	decay (noun)
destruction achieved by causing something to be wrecked or ruined	the organic phenomenon of rotting
a ruined building	a gradual decrease; as of stored charge or current
an event that results in destruction	the process of gradually becoming inferior
failure that results in a loss of position or reputation	the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
the process of becoming dilapidated	an inferior state resulting from the process of decaying
an irrecoverable state of devastation and destruction

ruin (verb)	decay (verb)
fall into ruin	fall into decay or ruin
destroy completely; damage irreparably	lose a stored charge, magnetic flux, or current
reduce to ruins	undergo decay or decomposition
deprive of virginity
reduce to bankruptcy
destroy or cause to fail