worsening vs diminution

worsening and diminution both are nouns.

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

As nouns, diminution is a hypernym of worsening; that is, diminution is a word with a broader meaning than worsening:

Other hypernyms of worsening include decline.

worsening (noun)	diminution (noun)
changing something with the result that it becomes worse	the act of decreasing or reducing something
process of changing to an inferior state	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower

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