shrinking vs diminution

shrinking and diminution both are nouns.

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

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

Other hypernyms of shrinking include decrease, reduction, step-down.

shrinking (noun)	diminution (noun)
the act of becoming less	the act of decreasing or reducing something
process or result of becoming less or smaller	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower