tax income vs taxation

tax income and taxation both are nouns.

Word	Noun	Adjective	Verb	Adverb
tax income	Yes	No	No	No
taxation	Yes	No	No	No

As nouns, tax income and taxation are synonyms defined as:

Other synonyms of tax income include revenue, tax revenue.

tax income (noun)	taxation (noun)
government income due to taxation	the imposition of taxes; the practice of the government in levying taxes on the subjects of a state
	charge against a citizen's person or property or activity for the support of government
	government income due to taxation