worsening vs decline in quality

worsening and decline in quality both are nouns.

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

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

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

Other synonyms of worsening include declension, deterioration.

worsening (noun)	decline in quality (noun)
changing something with the result that it becomes worse	process of changing to an inferior state
process of changing to an inferior state

worsening (adjective)	decline in quality (adjective)
changing for the worse