decline in quality vs deterioration

decline in quality and deterioration both are nouns.

Word	Noun	Adjective	Verb	Adverb
decline in quality	Yes	No	No	No
deterioration	Yes	No	No	No

As nouns, decline in quality and deterioration are synonyms defined as:

decline in quality and deterioration: process of changing to an inferior state

Other synonyms of decline in quality include declension, worsening.

decline in quality (noun)	deterioration (noun)
process of changing to an inferior state	process of changing to an inferior state
	a symptom of reduced quality or strength