tax evasion vs nonpayment

tax evasion and nonpayment both are nouns.

Word	Noun	Adjective	Verb	Adverb
tax evasion	Yes	No	No	No
nonpayment	Yes	No	No	No

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

tax evasion: the deliberate failure to pay taxes (usually by making a false report)
nonpayment: the deliberate act of failing to pay money

Other hypernyms of tax evasion include evasion.

tax evasion (noun)	nonpayment (noun)
the deliberate failure to pay taxes (usually by making a false report)	the deliberate act of failing to pay money
	loss resulting from failure of a debt to be paid
	act of failing to meet a financial obligation