SUPERTAX
surtax, supertax
(noun) an additional tax on certain kinds of income that has already been taxed
Source: WordNet® 3.1
Etymology
Noun
supertax (plural supertaxes)
An additional tax on something that has already been taxed
A higher rate of an existing tax
Source: Wiktionary
Su"per*tax`, n. [Super- + tax.]
Definition: A tax in addition to the usual or normal tax; specif., in the
United Kingdom, an income tax of sixpence for every pound in addition
to the normal income tax of one shilling and twopence for every
pound, imposed, by the Finance Act of 1909-1910 (c. 8, ss 66, 72), on
the amount by which the income of any person exceeds £3,000 when his
total income exceeds £5,000.
Source: Webster’s Unabridged Dictionary 1913 Edition