tax shelter vs diminution

tax shelter and diminution both are nouns.

Word	Noun	Adjective	Verb	Adverb
tax shelter	Yes	No	No	No
diminution	Yes	No	No	No

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

tax shelter: a way of organizing business to reduce the taxes it must pay on current earnings
diminution: the act of decreasing or reducing something

Other hypernyms of tax shelter include decrease, reduction, step-down.

tax shelter (noun)	diminution (noun)
a way of organizing business to reduce the taxes it must pay on current earnings	the act of decreasing or reducing something
	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower