IPA: //ˈsuːpərtæks//
KK: /ˈsuːpərtæks/
A higher rate of tax that is added on top of an existing tax, or an extra tax on something that has already been taxed.
The government introduced a supertax to increase revenue from wealthy individuals.
Supertax is formed from "super-" (meaning above or over) and "tax" (from Latin "taxare", meaning to assess or estimate). The word refers to a tax that is levied in addition to the standard tax, thus being an additional or higher tax.
Think of 'super-' meaning 'above' and 'tax' meaning 'to assess' — a supertax is an additional assessment on top of the regular tax.