tax credit vs diminution

tax credit and diminution both are nouns.

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

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

tax credit: a direct reduction in tax liability (not dependent on the taxpayer's tax bracket)
diminution: the act of decreasing or reducing something

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

tax credit (noun)	diminution (noun)
a direct reduction in tax liability (not dependent on the taxpayer's tax bracket)	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