surtax vs supertax

surtax and supertax both are nouns.

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

As nouns, surtax and supertax are synonyms defined as:

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

surtax (noun)	supertax (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

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