supertax vs surtax

supertax and surtax both are nouns.

Word	Noun	Adjective	Verb	Adverb
supertax	Yes	No	No	No
surtax	Yes	No	Yes	No

As nouns, supertax and surtax are synonyms defined as:

supertax and surtax: an additional tax on certain kinds of income that has already been taxed

supertax (noun)	surtax (noun)
an additional tax on certain kinds of income that has already been taxed	an additional tax on certain kinds of income that has already been taxed

supertax (verb)	surtax (verb)
	levy an extra tax on