decay vs deterioration

decay and deterioration both are nouns.

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

As nouns, deterioration is a hyponym of decay; that is, deterioration is a word with a more specific, narrower meaning than decay:

Other hyponyms of decay include putrefaction, rot, decomposition, disintegration, impairment, rancidity.

decay (noun)	deterioration (noun)
the organic phenomenon of rotting	process of changing to an inferior state
a gradual decrease; as of stored charge or current	a symptom of reduced quality or strength
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)	deterioration (verb)
fall into decay or ruin
lose a stored charge, magnetic flux, or current
undergo decay or decomposition