ad valorem tax vs excise tax

ad valorem tax and excise tax both are nouns.

Word	Noun	Adjective	Verb	Adverb
ad valorem tax	Yes	No	No	No
excise tax	Yes	No	No	No

As nouns, excise tax is a hypernym of ad valorem tax; that is, excise tax is a word with a broader meaning than ad valorem tax:

ad valorem tax: a tax levied on the difference between a commodity's price before taxes and its cost of production
excise tax: a tax that is measured by the amount of business done (not on property or income from real estate)

Other hypernyms of ad valorem tax include excise.

ad valorem tax (noun)	excise tax (noun)
a tax levied on the difference between a commodity's price before taxes and its cost of production	a tax that is measured by the amount of business done (not on property or income from real estate)