supertax vs income tax

supertax and income tax both are nouns.

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

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

supertax: an additional tax on certain kinds of income that has already been taxed
income tax: a personal tax levied on annual income

supertax (noun)	income tax (noun)
an additional tax on certain kinds of income that has already been taxed	a personal tax levied on annual income