tax credit vs reduction

tax credit and reduction both are nouns.

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

As nouns, reduction is a hypernym of tax credit; that is, reduction 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)
reduction: the act of decreasing or reducing something

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

tax credit (noun)	reduction (noun)
a direct reduction in tax liability (not dependent on the taxpayer's tax bracket)	the act of decreasing or reducing something
	the act of reducing complexity
	any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent