tax shelter vs decrease

tax shelter and decrease both are nouns.

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

As nouns, decrease is a hypernym of tax shelter; that is, decrease 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
decrease: the act of decreasing or reducing something

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

tax shelter (noun)	decrease (noun)
a way of organizing business to reduce the taxes it must pay on current earnings	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

tax shelter (verb)	decrease (verb)
	decrease in size, extent, or range
	make become smaller