From Longman Dictionary of Contemporary Englishsurtaxsur‧tax /ˈsɜːtæks $ ˈsɜːr-/ noun [uncountable] PETan additional tax on money you earn if it is higher than a particular amount
Examples from the Corpus
surtax• Until 1969, interest on bank loans as well as on mortgages was eligible for income tax and surtax relief.• Early polls showed a majority of Californians favored the surtax.From Longman Business Dictionarysurtaxsur‧tax /ˈsɜːtæksˈsɜːr-/ noun [countable, uncountable]TAX an additional tax paid by people or companies with a high level of incomesurtax onThere are plans to impose a 10% surtax on incomes of more than $100,000.Origin surtax (1800-1900) French surtaxe, from sur- ( → SURCHARGE) + taxe “tax” 