taxation vs imposition

taxation and imposition both are nouns.

Word	Noun	Adjective	Verb	Adverb
taxation	Yes	No	No	No
imposition	Yes	No	No	No

As nouns, imposition is a hypernym of taxation; that is, imposition is a word with a broader meaning than taxation:

taxation: the imposition of taxes; the practice of the government in levying taxes on the subjects of a state
imposition: the act of imposing something (as a tax or an embargo)

Other hypernyms of taxation include infliction.

taxation (noun)	imposition (noun)
the imposition of taxes; the practice of the government in levying taxes on the subjects of a state	the act of imposing something (as a tax or an embargo)
charge against a citizen's person or property or activity for the support of government	an uncalled-for burden
government income due to taxation