worsening vs declension

worsening and declension both are nouns.

Word	Noun	Adjective	Verb	Adverb
worsening	Yes	Yes	No	No
declension	Yes	No	No	No

As nouns, worsening and declension are synonyms defined as:

Other synonyms of worsening include decline in quality, deterioration.

worsening (noun)	declension (noun)
changing something with the result that it becomes worse	a class of nouns or pronouns or adjectives in Indo-European languages having the same (or very similar) inflectional forms
process of changing to an inferior state	a downward slope or bend
	process of changing to an inferior state
	the inflection of nouns and pronouns and adjectives in Indo-European languages

worsening (adjective)	declension (adjective)
changing for the worse